Gonadal histology was investigated by means of conventional microscopy in 6 patients with complete androgen insensitivity syndrome, in 11 with incomplete androgen insensitivity syndrome, and in 3 with 5\g=a\-reductase syndrome. Twelve subjects were prepubertal and 8 pubertal. In all patients gonadal tissue was removed as a prophylactic measure and no patients gave rise to any clinical suspicion of a tumour. Eight patients with incomplete androgen insensitivity syndrome, 5 of whom (62.5%) were prepubertal, showed intratubular germ cell neoplasia and in 6 of them it was bilateral. Histochemical and immunohistochemical analysis showed considerable agreement between atypical morphological aspects and positive response to Schiff's periodic acid and to staining with the anti-placenta alkaline phosphatase antibody. Our patients were characterized by one of the highest reported incidences of intratubular germ cell neoplasia, particularly at prepubertal age. These findings would seem to indicate that a rethink is needed concerning the general opinion that patients with androgen intensivity syndrome have practically no risk of developing malignancy, and that orchidectomy is not advisable before puberty is completed. It has long been recognized that patients with an¬ drogen insensitivity syndrome have a higher inci¬ dence of germ cell tumours (1,2) in adulthood.Recent studies (3-5) have pointed out that some subjects with this syndrome already have intratu¬ bular germ cell neoplasia patterns in childhood, and similar cellular changes in the gonads of infer¬ tile and cryptorchid men have been shown to be a true precursor of invasive tumours (6-11).In order to investigate the incidence of this condition in prepubertal patients and to evaluate its diagnostic implications, we examined the gonadal histology of 20 children and adolescents with male pseudohermaphroditism.