Drug related problems (DRP) are health problems associated with the pharmacological treatment of patients and interfere or can interfere with the expected results on their health. The aim of this study is to determine the prevalence of DRP in patients from an urban health centre that lead to hospitalisation, and its prevention.It is a retrospective, observational and descriptive study.Les Corts Health Centre (HC), which is an urban health and teaching centre with a reference population of 32,318 inhabitants.Users of the les Corts HC admitted to the Barcelona Hospital Clinic from August 2005 to January 2006. RESULTS AND MAIN OUTCOME MEASUREMENTS: A pharmacist and a family doctor analysed the clinical histories and determined whether or not there was a DRP. A DRP was present in 13.4% of all hospital discharges, and 12% were implicated in the hospital admission. It was considered that 57.3% of all the discharges with a DRP as the causing factor in the hospital admission were avoidable. Admissions due to DRP were mainly in internal medicine, cardiology and pneumology. The health problems that lead to hospital admission due to DRP are mainly circulatory (38.5%) and respiratory (11.5%).The number of hospital admissions due to drug related problems is avoidably high.