Maternal vitamin supplementation has been linked to a reduced risk of several pediatric malignancies. We examined this relationship in a study of childhood germ cell tumors (GCT). Subjects included 278 GCT cases diagnosed <15 years during 1993 to 2001 at a United States or Canadian Children's Oncology Group Institution and 423 controls that were ascertained through random digit dialing matched to cases on sex, and age within 1 year. Unconditional logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (CI) for the association between GCTs and maternal vitamin use at several time points during and around pregnancy. In models controlling for the child's age, sex, household income, and maternal education, any maternal vitamin use during the 6 months before conception through nursing was associated with a nonsignificant reduced risk of GCTs (OR, 0.7; 95% CI, 0.4-1.2). Inverse associations were observed for both extragonadal (OR, 0.8; 95% CI, 0.4-1.6) and gonadal (OR, 0.6; 95% CI, 0.3-1.1) tumors, and for dysgerminoma/seminoma (OR, 0.6; 95% CI, 0.2-1.3) and teratoma (OR, 0.5; 95% CI, 0.2-0.9) but not yolk sac tumors (OR, 1.1; 95% CI, 0.5-2.3). No consistent patterns were found with respect to vitamin use during the periconceptional period (6 months before pregnancy and first trimester) or first trimester specifically. In conclusion, although our study suggests that maternal vitamin supplementation may reduce the risk or pediatric GCTs in the offspring, the small study size and limitations inherent to observational studies must be considered when interpreting these results.