Purpose: To determine the risk factors on hospital mortality in patients with community-acquired severe sepsis and septic shock in the first 24 hours after admission to the intensive care unit. Materials and methods: The study was prospective, observational, singlecentre and included adult patients with community-acquired severe sepsis and septic shock. Demographics, clinical, laboratory and microbiological data were recorded. The main outcome measure was hospital mortality. Results: During the study period, 184 patients were included. The overall mortality rate was 51.6%, 44.4% with severe sepsis and 71.4% in patients with septic shock. The lung was the most common site of infection (65.8%) and respiratory failure was the most common organ failure (54.9%). Multivariate analysis identified four independent risk factors for mortality in patients with severe sepsis and septic shock: three or more organ dysfunctions (OR, 3.212; 95% CI, 1.585–6.506; p < 0.001), acute respiratory failure (OR, 2.649 95% CI, 1.327–5.287; p = 0.006), positive blood culture (OR, 2.708; 95% CI, 1.289–5.689; p = 0.009) and chronic heart failure (OR, 2.112; 95% CI, 1.036–4.308; p = 0.040). Conclusion: Our results highlight the importance of three or more organ dysfunctions, acute respiratory failure, positive blood culture and chronic heart failure as independent risk factors for mortality in the first 24 hours after admission in patients with severe sepsis and septic shock. This will benefit the early identification of patients at high risk for poor outcomes that contributes to intensive management and appropriate treatment interventions. [ABSTRACT FROM AUTHOR]