FSH and insulin are key hormones involved in spontaneous ovulation. Adolescent girls born small for gestational age (SGA) are at risk for FSH and insulin resistance. We have assessed whether ovulation rate is reduced in SGA girls. Ovulatory function was assessed by weekly filter paper progesterone measurements, obtained by finger-stick auto-sampling for 3 consecutive months in matched populations of asymptomatic, nonobese girls (mean age, 15.5 yr; > or =3 yr postmenarche) who were either born with an appropriate weight for gestational age (AGA; n = 24; mean birthweight, 3.3 kg) or born small for gestational age (SGA; n = 25; mean birthweight, 2.3 kg). The prevalence of anovulation was higher among SGA than AGA girls (40% vs. 4%; P = 0.002). Moreover, in the relatively small fraction of ovulating SGA girls, the ovulation rate was lower than in AGA adolescents (average number of ovulations during the study, 1.4 vs. 1.9; P < 0.01). In conclusion, the endocrine correlates of prenatal growth restraint are herewith extended to include oligo-ovulation and anovulation in adolescence. It remains to be verified whether this SGA-related phenomenon persists into the reproductive age range. If it does, then fetal growth restraint may prove to be one of the enigmatic components underpinning hitherto unexplained female subfertility.