Background: The UK has the highest rate of teenage pregnancies in western Europe. Although there is a large body of literature focusing on predictors of conception among this age group, almost all the work compares those young women who have become pregnant with their peers, regardless of whether or not their peers have experienced sexual intercourse. Objective: To compare 16-year-old young women who have become pregnant with their peers who also have experience of sexual intercourse, but who have not conceived. Design: Analysis of data from the baseline and follow-up surveys conducted as part of a trial of sex education. Setting and participants: Female school students aged 14-16 years from the East of Scotland. Main results: Young age of self and partner, and non-use of contraception, all at first intercourse, are most strongly associated with pregnancy. Conclusions: Those who engage in sexual intercourse at a relatively young age will often have had more opportunity to become pregnant than those whose sexual debut comes later. Similarly, the fact that those who use contraception at first intercourse have been less likely to conceive than those who do not could reflect the overall patterns of contraceptive use: young women who have used contraception at each occasion of intercourse will have had less chance to conceive than those who have not. Having a young partner at first intercourse suggests that, if this pattern continues, the couple may lack the resources needed to prevent a pregnancy due to the immaturity of both partners.