Allergic contact dermatitis (ACD) and photo-ACD are cell-mediated delayed hypersensitivity reactions of the skin caused by a wide range of substances. Topical ketoprofen (KP), a nonsteroidal anti-inflammatory drug (NSAID), can induce ACD and photo-ACD. Patients with ACD and/or photo-ACD to KP frequently show concomitant sensitization to other substances. The aim of this study was to identify the substances most frequently associated with sensitization to KP, and to evaluate, by means of computerized conformational analysis, whether this association could be due to crossallergy. 15 subjects with ACD and photo-ACD to KP were tested with the SIDAPA (Societa Italiana di Dermatologia Allergologica Professionale ed Ambientale) patch test standard series, including fragrance mix and its components (eugenol, isoeugenol, oak moss, geraniol, hydroxycitronellal, amylcinnamaldehyde, cinnamyl alcohol and cinnamaldehyde) and with the SIDAPA photopatch test series. Allergic reactions to cinnamyl alcohol were noted in all patients, whereas some patients also showed positive reactions to fenticlor, octocrylene and benzophenone-10. Computerized conformational analysis demonstrated that the structure of cinnamyl alcohol is similar to that of KP, whereas the structures of benzophenone-10, octocrylene and fenticlor are completely different. These results suggest that in patients with contact allergy to KP, concomitant positive reactions to cinnamyl alcohol are due to cross-sensitization, whereas simultaneous allergic reactions to fenticlor, octocrylene and benzophenone-10 should be regarded as cosensitizations.