OBJECTIVE The study was undertaken to determine the outcome of singleton pregnancies conceived through ovulation induction and intrauterine insemination using a partner's (OI/IUI) or donor sperm (OI/IUID) by comparison with naturally conceived singletons within a national cohort. METHODS Retrospective cohort study in primigravid women who were treated with OI/IUI (n = 97) or OI/IUID (n = 35) at Glasgow Royal Infirmary between March 1993 and March 1997 and identified within the Scottish national cohort (n = 109,443) delivering during the same period. Univariate and multivariate logistic regression models were used to examine outcomes and to determine the factors associated with infertility treatment and low birth weight. RESULTS OI/IUI singletons were more likely to be lighter, of clinically low birth weight, and born more prematurely than natural conceptions. After adjustment for associated factors, these infants were 4.85 times (95% CI 2.25-10.48) more likely to be of low birth weight. We could not demonstrate any differences between OI/IUID and natural conceptions. CONCLUSIONS The perinatal outcome of singletons born to subfertile mothers conceived through OI/IUI is poorer than that of matched natural conceptions. We suggest that intrinsic factors in subfertile couples predispose them to having smaller infants and that "infertility" should be added to the list of recognized factors associated with low birth weight.