Objectives In the elderly population, chronic diseases are common determinants of mobility limitations and comorbidity consistently shows a strong association with functional status. This study was designed to evaluate the role of single chronic diseases and of their combination on functional recovery after rehabilitative treatment in disabled elderly patients. Design With respect to the difference in magnitude of their disabling effect, diseases were classified into 2 groups: “more disabling” diseases (COPD, heart failure, peripheral artery diseases, diabetes, and not life-threatening cancer) and “less disabling” diseases (anemia, kidney, gastrointestinal, and liver diseases). Setting 35-bed Geriatric Evaluation and Rehabilitation Unit. Participants We studied 710 patients (age 77.8 ± 7.4 years, 76.2% females), consecutively admitted for stroke, Parkinson’s disease, and osteoarthritis. Measurements A multidimensional evaluation for mobility (Tinetti-score), cognitive status (MMSE), and somatic health (Greenfield’s Individual Disease Severity Index-IDS, Burden of diseases-BoD) was performed. Functional recovery was decided based on the Delta-Tinetti, which is the difference of the values between admission and discharge. Results We tested, in a multivariate regression model, the predictive role of single chronic conditions and of their combinations on functional recovery, after having adjusted for which diseases are direct causes of disability (stroke, Parkinson’s disease, and osteoarthritis) and other potential predictors (age, sex, cognitive function, depressive symptoms, albumin, and c-reactive protein). A negative prediction of functional recovery was expressed by the “more disabling” diseases group. The determinants of poor recovery were characterized by the combination of “more disabling diseases” rather than single condition effects, independently by age, cognitive, and functional status on admission. Conclusion Our study adds a new perspective about the role of COPD, heart failure, peripheral artery diseases, diabetes and not life-threatening cancer on functional recovery, emphasizing their combined impact in elderly people.