Previous studies have suggested that pregnancy measures of insulin-like growth factors (IGFs) may be related to breast cancer risk in mothers. IGFs may also be important in cervical cancer etiology. We conducted a nested case-control study (69 breast cancer cases, 151 cervical cancer cases, 443 controls) among mothers of the Avon Longitudinal Study of Parents and Children (ALSPAC) cohort. Over 70% of blood samples was taken prior to 15 weeks' gestation; the remainder before 30 weeks. Logistic regression, controlling for maternal age, gestational age, and sample type (plasma/serum) was used to model the association between IGFs and maternal cancer risk. Neither IGF-I nor IGF-II were associated with breast or cervical cancer. IGF-binding protein (BP)-3 was not related to breast cancer, but there was a suggestion that women in the highest compared to lowest quartile of IGFBP-3 had reduced risk of cervical cancer, OR 0.43 (95% CI 0.21-0.86). In conclusion, the importance of IGFs measured in pregnancy and later breast and cervical cancer remains unclear, though IGFBP-3 may be a marker of lowered risk.