Background The leading causes of mortality globally in children younger than five years of age (under‐fives), and particularly in the regions of sub‐Saharan Africa (SSA) and Southern Asia, in 2018 were infectious diseases, including pneumonia (15%), diarrhoea (8%), malaria (5%) and newborn sepsis (7%) (UNICEF 2019). Nutrition‐related factors contributed to 45% of under‐five deaths (UNICEF 2019). World Health Organization (WHO) and United Nations Children's Fund (UNICEF), in collaboration with other development partners, have developed an approach – now known as integrated community case management (iCCM) – to bring treatment services for children 'closer to home'. The iCCM approach provides integrated case management services for two or more illnesses – including diarrhoea, pneumonia, malaria, severe acute malnutrition or neonatal sepsis – among under‐fives at community level (i.e. outside of healthcare facilities) by lay health workers where there is limited access to health facility‐based case management services (WHO/UNICEF 2012). Objectives To assess the effects of the integrated community case management (iCCM) strategy on coverage of appropriate treatment for childhood illness by an appropriate provider, quality of care, case load or severity of illness at health facilities, mortality, adverse events and coverage of careseeking for children younger than five years of age in low‐ and middle‐income countries. Search methods We searched CENTRAL, MEDLINE, Embase and CINAHL on 7 November 2019, Virtual Health Library on 8 November 2019, and Popline on 5 December 2018, three other databases on 22 March 2019 and two trial registers on 8 November 2019. We performed reference checking, and citation searching, and contacted study authors to identify additional studies. Selection criteria Randomized controlled trials (RCTs), cluster‐RCTs, controlled before‐after studies (CBAs), interrupted time series (ITS) studies and repeated measures studies comparing generic WHO/UNICEF iCCM (or local adaptation thereof) for at least two iCCM diseases with usual facility services (facility treatment services) with or without single disease community case management (CCM). We included studies reporting on coverage of appropriate treatment for childhood illness by an appropriate provider, quality of care, case load or severity of illness at health facilities, mortality, adverse events and coverage of careseeking for under‐fives in low‐ and middle‐income countries. Data collection and analysis At least two review authors independently screened abstracts, screened full texts and extracted data using a standardised data collection form adapted from the EPOC Good Practice Data Collection Form. We resolved any disagreements through discussion or, if required, we consulted a third review author not involved in the original screening. We contacted study authors for clarification or additional details when necessary. We reported risk ratios (RR) for dichotomous outcomes and hazard ratios (HR) for time to event outcomes, with 95% confidence intervals (CI), adjusted for clustering, where possible. We used estimates of effect from the primary analysis reported by the investigators, where possible. We analysed the effects of randomized trials and other study types separately. We used the GRADE approach to assess the certainty of evidence. Main results We included seven studies, of which three were cluster RCTs and four were CBAs. Six of the seven studies were in SSA and one study was in Southern Asia. The iCCM components and inputs were fairly consistent across the seven studies with notable variation for the training and deployment component (e.g. on payment of iCCM providers) and the system component (e.g. on improving information systems). When compared to usual facility services, we are uncertain of the effect of iCCM on coverage of appropriate treatment from an appropriate provider for any iCCM illness (RR 0.96, 95% CI 0.77 to 1.19; 2 CBA studies, 5898 children; very low‐certainty evidence). iCCM may have little to no effect on neonatal mortality (HR 1.01, 95% 0.73 to 1.28; 2 trials, 65,209 children; low‐certainty evidence). We are uncertain of the effect of iCCM on infant mortality (HR 1.02, 95% CI 0.83 to 1.26; 2 trials, 60,480 children; very low‐certainty evidence) and under‐five mortality (HR 1.18, 95% CI 1.01 to 1.37; 1 trial, 4729 children; very low‐certainty evidence). iCCM probably increases coverage of careseeking to an appropriate provider for any iCCM illness by 68% (RR 1.68, 95% CI 1.24 to 2.27; 2 trials, 9853 children; moderate‐certainty evidence). None of the studies reported quality of care, severity of illness or adverse events for this comparison. When compared to usual facility services plus CCM for malaria, we are uncertain of the effect of iCCM on coverage of appropriate treatment from an appropriate provider for any iCCM illness (very low‐certainty evidence) and iCCM may have little or no effect on careseeking to an appropriate provider for any iCCM illness (RR 1.06, 95% CI 0.97 to 1.17; 1 trial, 811 children; low‐certainty evidence). None of the studies reported quality of care, case load or severity of illness at health facilities, mortality or adverse events for this comparison. Authors' conclusions iCCM probably increases coverage of careseeking to an appropriate provider for any iCCM illness. However, the evidence presented here underscores the importance of moving beyond training and deployment to valuing iCCM providers, strengthening health systems and engaging community systems., Plain language summary Integrated community case management of childhood illness in low‐ and middle‐income countries What was the aim of this review? This Cochrane Review aimed to assess the effects of integrated community case management (iCCM) for children under‐five in low‐ and middle‐income countries. The review authors collected and analysed all relevant studies to answer this question and found seven studies. Key messages When iCCM is compared to usual facility services, it probably increases the number of parents who seek care from a healthcare worker. But we do not know if more children get the correct treatment, and it may have no effect on the number of children who die. What was studied in the review? Each year, more than five million children die before the age of five. Most of these children live in sub‐Saharan Africa or Central and Southern Asia. Many of these children suffer from infectious diseases including pneumonia and diarrhoea; and from malaria and malnutrition. And many children have more than one of these illnesses at the same time. These children do not always have easy access to healthcare services. To address these problems, the World Health Organization, United Nations Children's Fund (UNICEF) and others have developed an approach known as iCCM. iCCM focuses on children under five years of age living in rural and hard‐to‐reach areas. They receive services from lay health workers who are based in the community, outside of healthcare facilities. There are three main components of iCCM: – Lay health workers are trained to assess children's health, provide services for common childhood illnesses and refer children to healthcare facilities where necessary. (A lay health worker is a lay person who has received some training to deliver healthcare services but is not a health professional.) – Systems are put in place to make sure that the lay health workers have good access to supplies, get regular supervision and can easily refer children on to healthcare facilities. – Families and communities receive communication and information about good practices for health and nutrition. What were the main results of the review? The review authors found seven relevant studies. Six were from sub‐Saharan Africa and one was from Southern Asia. Some of the studies compared settings that had iCCM with settings that only had usual healthcare facilities. Some of the other studies compared settings that had iCCM with settings that had usual healthcare facilities as well as community‐based management of malaria. When iCCM is compared to usual facility services: – It probably increases the number of parents who seek care from a healthcare worker when their children have common childhood illnesses. – We do not know if more children get the correct treatment for childhood illnesses because the certainty of the evidence was very low. – There may be no effect on the number of newborn children who die. – We do not know what the effect is on the number of infants and children under‐five years who die. – We do not know what the effect is on quality of care, side effects or the number of children who attend healthcare facilities because the studies did not measure this. When iCCM is compared to usual facility services plus community‐based management of malaria: – It may have no effect on the number of parents who seek care from a healthcare worker when their children have common childhood illnesses. – We do not know if more children get the correct treatment for childhood illnesses because the certainty of the evidence was very low. – We do not know what the effect is on the number of children who die. – We do not know what the effect is on quality of care, side effects or the number of children who attend healthcare facilities because the studies did not measure this. How up‐to‐date is this review? The review authors searched for studies that had been published up to 7 November 2019.