One thousand and forty one Senior secondary School Students in Ilorin, Kwara State, Nigeria were surveyed using a 117-items self-administered substance use questionnaire in May 1988. Males constituted 56.6% and Females 43.5% of the study population. The mean age was 16.8 years (S.D. 1.84). The most currently used substances were found to include salicylate analgesics (56.2%), antibiotics (23.6%), stimulants (21.6%), alcohol (12.0%) and cigarette (4.4%). Current use of alcohol, antibiotics and salicylate analgesic was significantly more common in the rural school. Current use of cigarette and cannabis occurred significantly more in the male population while no significant sex differences were noted for the other drugs surveyed. For many students, initiation into substance use started at primary school level. The need to monitor the pattern of substance use at all levels of our educational system (primary, secondary and post-secondary) and to develop adequate preventive programmes for the student population was emphasized.