OBJECTIVE The aim was to survey oral contraceptive usage among women under 25 years of age. METHODS This was a cross sectional population study based on information collected by questionnaire mailed to randomly selected individuals. METHODS The study population consisted of Swedish women born between 1960 and 1964 and living in the southern Swedish health care region which has about one and a half million inhabitants. METHODS The sample consisted of 3477 women, of whom 2573 or 74% agreed to participate in the study and were interviewed between November 1990 and April 1991. RESULTS Of the 2573 women participating, 2254 (88%) reported having used oral contraceptives at some time, 77% of them having started during their teens. Teenage start of oral contraceptive use was found to be related to a lower age at menarche, a higher marriage/cohabitation rate, a lower rate of teenage full term pregnancy, a higher rate of spontaneous abortion, a lower frequency of teetotalism, and a higher frequency of smoking. Longterm use of antipsychotic drugs appeared to be less common among women who started oral contraceptive use early, but no relationship with other pharmaceutical drug usage was found. No relationship was found between oral contraceptive use and the presence of a first degree relative with cancer. CONCLUSIONS A large proportion of Swedish women start using oral contraceptives during their teens, and report long duration of usage both before their first full term pregnancy and before the age of 25 years. The few women who have never used oral contraceptives do not appear to be representative of the general population.