OBJECTIVE To describe adverse drug events (ADEs) in children under intensive care, identify risk factors and tools that can detect ADEs early, and the impact on length of stay (LOS). METHODS A prospective observational study. METHODS Paediatric intensive care unit of a tertiary care teaching hospital. METHODS 239 patients with a mean age of 67.5 months representing 1818 days of hospitalisation in intensive care unit. METHODS Active search of charts and electronic patient records using triggers. The statistical analysis involved linear and logistic regression. RESULTS The average LOS was 7.6 days. There were 110 proven, probable and possible ADEs in 84 patients (35.1%). We observed 138 instances of triggers. The major classes of drugs associated with events were: antibiotics (n=41), diuretics (n=24), antiseizures (n=23), sedatives and analgesics (n=17) and steroids (n=18). The number of drugs administered was most related to the occurrence of ADEs and also to the LOS (p<0.001). The occurrence of an ADE may result in an increase in the LOS by 1.5 days per event, but this was not statistically significant in this sample. Patients aged less than 48 months also proved to be at a significant risk for ADEs, with an OR of 1.84 (95% CI 1.07 to 3.15, p=0.025). The number of drugs administered also correlated with the number of ADEs (p<0.0001). The chance of having at least one ADE increased linearly as the patient was administered more drugs. CONCLUSIONS The use of multiple drugs as well as lower patient age favours the occurrence of ADEs. The active search described here provides a systematic approach to this problem.