To evaluate the extent and motivations of self-medication, a survey was conducted among 376 adolescents aged 15 to 20 using both written questionnaires and face-to-face interviews. 84% reported having taken some drug during the preceding 15 days, 57% on their own initiative. The most frequently cited drugs were analgesics, vitamins, homeopathy and anti-inflammatory drugs. Psychotropics had been taken by 7% (as self-medication by 3%). Street drugs, mainly cannabis derivatives, had been taken by 18%. The most usual indications for self-medication were headaches (42%), influenza-like syndromes (31%), school-related stress (21%), fatigue (19%) and mood concerns (15%). Most drugs were obtained from family reserves. A multivariate analysis showed self-medication to be associated with complaints regarding headaches, past drug dependency, concerns about illegal drugs or family interactions, recent respiratory illness, and diurnal somnolence. Self-medication increased with age. There was no relationship between self-medication and gender, citizenship, parental education level, or parental drug taking. Nor was self-medication related to knowledge about pharmaceuticals, assessed by specific questions. These results support the interpretation of self-medication mainly as a learned response to psychic/somatic ill-being. An optimal utility/risk ratio for self-prescribed drugs would require public health action and global involvement of practitioners.