Cytogenetic studies in eight patients with male pseudohermaphrodism, not of the testicular feminization type, are reported. Sex-Chromosome mosaicism was observed in six of the eight patients. XO/XY mosaicism was found to persist in one of the patients over an observation period of eight years. In general, the presence of XO cells affected the physical characteristics of the patients, particularly longitudinal growth. Three of the patients attained pubertal age and virilized; however, all had evidence of partial testicular failure. The brother of one of the two patients without mosaicism (XY) had a severe degree of hypospadias, suggesting a familial tendency toward abnormal sexual differentiation in the males.