A child with ambiguous genitalia was born after an uncomplicated pregnancy. Laparotomy revealed intraabdominal hypoplastic testes containing normal appearing Leydig cells; germ cells were present in the left gonad, not in the right. The karyotype was 46,XY in blood leukocytes and in fibroblasts cultured from the gonads; there was no evidence of mosaicism. Endocrinologic study revealed no disorder of steroidogenesis. Androgen receptors were not studied. Serologic evaluation of blood leukocytes revealed the presence of H-Y antigen, but there are reasons to believe that less H-Y antigen was present in the cells of the patient than was present in corresponding cells from normal males. Gonadectomy and clitoral recession were performed at 3 weeks of age, and the patient was reared as a girl. We speculate that reduced expression of H-Y may have induced aberrant development of the gonads.