A 3-month-old female infant feminized by an ovarian stromal tumor is presented. Clinicopathologic aspects of such tumors occurring in infancy are discussed. In addition, the evaluation of hypothalamic-pituitary function preoperatively and postoperatively are presented. In the preoperative, high-steroid environment, both basal and stimulated secretion of follicle-stimulating hormone (FSH) was suppressed. Secretion of luteinizing hormone (LH) was normal. Following surgical castration, stimulated secretion of both gonadotropins clearly increased. These findings suggest an active but less sensitive negative feedback mechanism for FSH than for LH during infancy, i.e., high concentrations of gonadal steroids are necessary to maximally suppress FSH secretion while normal steroid concentrations appear to maximally suppress LH secretion. Developmental changes in hypothalamic-pituitary sensitivity to negative feedback controls are discussed in light of these findings.