OBJECTIVE To measure the prevalence of sexually transmitted diseases (STD), pelvic inflammatory disease (PID), cervical cancer, pregnancy and use of contraception in teenagers, and to determine socioeconomic factors associated with these conditions to aid planners of medical services and promotion of sexual health. METHODS 181 Ethiopian teenagers and 1,845 women aged 20 to 45 years for comparison. METHODS Gynaecological outpatient department, antenatal, postnatal and family planning clinics, in two teaching hospitals and a mother and child heath centre in Addis Ababa, Ethiopia. METHODS Results of serologic tests for STD, clinical evidence of PID, and cervical cytology were analysed against socio-economic factors. RESULTS In teenagers early age at first marriage/coitus, more common in those of rural origin, was associated with poverty, a greater number of lifetime sexual partners, and prostitution: 40 pc were first sexually active before the menarche. Prevalence of seropositivity to specific STD pathogens was; Treponema pallidum (TPHA) 21 pc, Neisseria gonorrhoeae (gonococcal antibody test: GAT) 40 pc, genital chlamydiae 51 pc, hepatitis B virus 36 pc, herpes simplex virus (HSV-2) 32 pc, and Haemophilus ducreyi 16 pc: 92 pc of teenagers were seropositive to one or more STD's. STD seroprevalence was higher in those with more than one sexual partner, those sexually active by age 15 (very high in those sexually active by age 12), those involved in prostitution and those attending the family planning clinic. Forty three pc had clinical evidence of PID; one married at age 10 had invasive cervical cancer by age 18; 40 pc of teenagers were pregnant compared with 25 pc of those aged 20 to 45; 21 pc attended for family planning; of regular FPC attenders 81 pc were GAT seropositive. CONCLUSIONS Despite legislation early age of sexual debut is common, STD and PID are widely prevalent, the pregnancy rate in adolescents is high and contributes to the national population growth rate. Action is required at family, medical and governmental level to encourage cultural acceptance that marriage and sexual activity should not occur before the age of 16 years, with education appropriate to culture to prevent STD. Similar studies are recommended in other countries to establish a baseline for informed strategy regarding prevention of STD and health education.