The use of topical non-steroidal anti-inflammatory drugs (NSAIDs) is very popular in spite of their doubtful efficacy and high number of generally not serious, but preventable, adverse effects, especially photoallergy. The allergenic potential of different topical NSAIDs was determined by performing a retrospective observational study of the period 1996-2001 and comparing the cases of allergy and photoallergy with the use of each topical NSAID. The diagnoses were obtained from a review of the clinical records of patch/photopatch testing carried out in the dermatology departments of 2 public hospitals in Bizkaia (Spain). The use of the different topical NSAIDs was obtained from invoices sent to the National Health System and the Reporting odds ratio (ROR) and Proportional reporting ratio (PRR) disproportionality estimates of the FEDRA database of the Spanish Pharmacovigilance System. A total of 139 contact reactions to topical NSAIDs were found with ketoprofen being responsible for 28% of the allergies and 82% of the contact photoallergies in spite of not being the most used topical NSAID (third in the ranking, diclofenac was the first). The ROR for ketoprofen was 3.9 (2.4-6.4) and the PRR 3.4 (2.1-5.5), thus confirming the possibility of a warning signal. The results support the need for regulatory action on topical ketoprofen.