Determining adverse event (AE) incidence, preventability, classification and impact for establishing their importance as a public health problem within the Colombian Social Security System.This was a study of a prospective inpatient cohort from three Colombian general-practice institutions.at least 12 hours' length of hospital stay during 2006.suffering psychiatric disorders and AE which had occurred before hospitalisation indexing. The sample consisted of 6 557 patients.clinical charts. Being a three-phase design, the first phase consisted of translating and standardising screening and causation formats, phase II of actively monitoring screening criteria and phase III of evaluating causation regarding the care being provided, based on specialist committee concept on a 0-6 scale. The variables measured were age, gender, social security affiliation, cumulative AE incidence, temporality, preventability of AE and disability resulting from them.6,688 patients were evaluated; 505 of them fulfilled positive screening criteria (95 % CI=7,9;7,3-8,6), 310 presented at least one AE during their hospitalisation (95 %CI for accumulated incidence=4,6; 4,1-5,1). AE were considered to have been preventable in 189 cases (95 % CI=61;55-66) and permanent disability occurred in 1,3 % of them. AE-associated mortality was 6,4 % (20/310). Hospitalisation became increased to 1 072 days as a direct consequence of AE.This study revealed an important incidence of AE in three Colombian hospitals, these being mainly preventable. Their ongoing monitoring as a part of risk management systems could reduce costs and AE-associated morbidity and mortality.