The Pharmacoepidemiologic Service of the Second University of Naples analyzed the use and tolerability of over-the-counter (OTC) oral nonsteroidal anti-inflammatory drugs (NSAIDs) purchased in Campania, a region of southern Italy. Forty private pharmacies uniformly distributed throughout the region were recruited. The study was conducted by means of a questionnaire completed by purchasers and lasted from December 1, 1999 to March 31, 2000; 2,053 questionnaires were collected. The age of respondents averaged 45.3 +/- 3.49 years (range, 17-85 years). The NSAIDs analyzed were acetylsalicylic acid, paracetamol, ibuprofen, ketoprofen, diclofenac, and piroxicam. Adverse effects, mainly gastrointestinal symptoms, were reported by 5.5% of the users and occurred primarily with diclofenac, piroxicam, ibuprofen, and ketoprofen. Because the use and availability of OTC NSAIDs are increasing, further studies of the tolerability of this important drug class are warranted.