A light microscopical study of an excised testis from a 14 1/2-year-old girl with incomplete type of testicular feminization syndrome revealed a carcinoma-in-situ pattern in a part of the gonad. An identical histological pattern has repeatedly been demonstrated in infertile men who developed gross testicular germ cell tumours. It is suggested that germ cell carcinomas in patients with testicular feminization syndrome may be preceded by this characteristic intratubular germ cell abnormality.