OBJECTIVE: To document the number and types of drug-related problems (DRPs) identified in customers purchasing nonprescription products in Swedish pharmacies; describe the distribution of DRPs by customer's gender, age, underlying ailment, and class of drug; determine whether problems are identified to the same extent in pharmacies with staffed nonprescription self-service departments as in pharmacies with over-the-counter sales; and document the number and types of pharmacy interventions to prevent or resolve DRPs, including reasons for drug switches and referrals to physicians. METHODS: A computerized instrument for documentation of DRPs and pharmacy interventions was developed. The study was conducted in 45 volunteer pharmacies in Sweden during 10 weeks in late 1999. RESULTS: A total of 1,425 problems and 2,040 interventions were recorded by 308 pharmacy practitioners. Relatively fewer DRPs were documented in pharmacies with self-service departments. The most common DRPs were uncertainty about the indication for the drug (33.5%) and therapy failure (19.5%). Dyspepsia was the most frequently specified symptom (11.4%). Consumers of dermatologic products had significantly higher rates of problems than expected in relation to sales volume. The most common ways of responding to a problem were with consumer drug counseling (61.1%), switching of drugs (43.9%), and referral to a physician (27.5%). CONCLUSIONS: The study has demonstrated a need for more professional attention and intervention by pharmacy staff to prevent and rectify DRPs in nonprescription consumers. It seems especially important to make sure that consumers receive the appropriate drugs for their current ailments.