Adolescence represents the period with the highest frequency of negative consequences associated with sexual activities (sexually transmitted diseases and unwanted pregnancies). An epidemiological study was carried out in symptomatic patients attending our Outpatient Clinic for Sexually Transmitted Diseases between April 1995 and April 1999 in order to evaluate the behaviour pattern of the adolescent population and identify the differences compared to the adult population.A questionnaire was used to assess the characteristics of two groups of patients: the first consisted of 54 teenagers (13-19 years-old) and the second, the control group, consisted of 917 women aged between 20 and 40 years old.A high percentage of pregnancies (22.2%) and voluntary abortions (41.6%) was observed in teenagers, associated with different sexual behaviours. The age of sexual intercourse was below 15 in 44.4% of adolescents (vs 7.7% of controls), whereas 61.1% had more than one sexual partner and 20.4% had changed partners in the last 6 months (vs 7.4%). 50% of teenagers did not use any method of contraception (vs 44.2%) and barrier methods were only used by 20.4% (vs 18.4%).Our study confirms the existence of a high-risk behavioural pattern in the adolescent population and draws attention yet again to the need for a serious programme of prevention and sexual education which will allow adolescents to experience the discovery of their own sexuality with greater awareness and safety.