The anatomic findings and gonadal histology of 41 patients who had atypical forms of gonadal dysgenesis or of male pseudohermaphroditism are described. Fourteen of these cases were classified as atypical gonadal dysgenesis because there were gross evidences of abnormal gonadal development, differing from those of classical Turner's syndrome. In this group there was no incidence of familial inheritance but there were evidences of chromosomal aberrations. Two patients diagnosed as [00BB]gonadal dysplasia[00AB] had primitive genital streaks differing from those of typical gonadal aplasia (Turner's Syndrome) only in the presence of masses of Leydig-like cells. That this condition is a variant of gonadal aplasia is suggested by the association of short stature in one case and by the demonstration in the other case of chromosomal mosaicism of XO/XX pattern, with the XO cell type predominant as in chromatin-negative Turner's Syndrome. Ten patients had [00BB]asymmetricalgonadal differentiation[00AB]with a testis on one side and on the other side either no gonad (2 cases), a primitive genital streak (6 cases) or an undifferentiated gonad