A structured computer-coded questionnaire was administered to 120 consecutive teenage mothers attending a public adolescent antenatal clinic in order to examine their sociodemographic characteristics and sexual behaviour, The mean age of teenagers attending the clinic was 17.7 years (range: 14-19); only 5 (4.1%) mere under 16 gears, The mean gestation at booking was 16.4 weeks (range: 6 34); 90 (75%) had unreliable menstrual dates; 29 (24.2%) were over 20 weeks, 18 (68.9%) of these saying that they were afraid to attend hospital earlier, Ninety seven (80.8%) said that they had just one sexual partner to date and 105 (87.5%) said that they were involved in a continuing relationship with the father of the baby Conception occurred within the first year of the relationship in 110 (91.6%). One hundred and seventeen (88.2%) were from social clases III-V 15 (12.5%) were still at secondary school and 59 (49.2%) were unemployed, Of the 105 (87.5%) who had left school 80% had not sat the Leaving Certificate and 10% had not undertaken any state examinations, Sixty seven (55.8%) continued to smoke and 29 (24.2%) to drink alcohol during pregnancy, Sixty two mothers (51.7%) had used contraception in the past; only 33 (27.5%) had used it always, The age of first coitus, fertility awareness and the use of contraception were significantly influenced by social class and education, This study highlights the necessity for early commencement of sexual education programmes.