To assess drug use and the incidence of mild to moderate adverse drug effects (AE) in children aged 0 - 16 years, with 2 different approaches. All 185 pediatric practices in the State of Brandenburg, Germany, were surveyed (95% positive response). A random sample of 50 practices servicing 36,000 children participated in the study as sentinel physicians reporting any AE among their patients. Twenty practices servicing 14,000 children were included in a drug utilization component (DUC) which documented diagnoses, prescribing and AE in all children seen in a 3-month period. The results on the DUC are based on 12,628 children with 26,168 physician contacts, 34,465 diagnoses and 33,140 drug prescriptions given to 85% of the children seen (average age: 6.7 years). Practice size ranged from 94 to 1,473 children seen in a 3-month period. The average number of physician contacts per child was 2. 1, with 10% seeing a physician 5 times and more. The diagnoses were respiratory ailments (30%), skin- (12%), injection- (11%) and trauma- (10%) related diagnoses. Major drug uses were respiratory (34% of prescriptions), anti-infective (22%), dermatological (13%), gastrointestinal (9%) and psychotropic agents (8%). One hundred and fifty-two AE affecting 150 children were documented in the DUC, 60% of these occurring within 3 days after treatment initiation. 83% of AE were mild (up to 4 on a scale from I -6), and 85% were considered by physicians to be attributable. Only 4 reports of very severe events were received. 47% of reports were related to antibiotic uses, 31% to immunizations, 11% to respiratory, and 4% to gastrointestinal agents. While there are no differences in the occurrence of AE by gender, AE decreases significantly by age, maintaining the same patterns of AE type and causative medication. Over a 3-month period, the incidence of mild to moderate ADR in children given medications is estimated as 1,200 per 100,000, or about 1%. Underreporting of AE remains an issue even when a monitoring scheme suggests compliance. The results of this study show that while AE in children are generally non-serious, 1% of treatments might elicit mild AE leading to a consultation. Direct practice recording produces more reports than a sentinel system.