OBJECTIVE: To identify the potential neoplastic risk in gonadal development abnormality with Y chromosome. METHODS: Inquiries about the illness history were made. Lymphocyte chromosomal karyotype of peripheral blood was analyzed. Sex determining region Y gene and relative steroids and enzymes were detected. Gonadal site was examined through medical imaging. Gonadal excision was performed by laparotomy or laparoscopy. Pathological examinations were done on all of the specimens. RESULTS: Among 41 cases of androgen insensitive syndrome, spermatogenic cell neoplasm occurred in 1 patient, sertoli cell tumor in 2, and interstitial cell hyperplasia in 5. Among 14 cases of 17 alpha-hydroxylase deficiency (XY) syndrome, one was sertoli cell tumor, and one was sertoli cell hyperplasia. In 4 cases of XY pure gonadal dysgenesis, one was gonadoblastoma with dysgerminoma. One of 16 cases of XO/XY gonadal dysgenesis was spermatogenic cell neoplasm with agenda cell tumor. Four cases of testes degeneration were all with dysgenetic testes. All of the gonadoblastoma and germ-cell tumor were located in the pelvis. Tumors occurred mostly during 15 years of age to 32 years. CONCLUSIONS: The gonads of XY pure gonadal dysgenesis has high risks of gonadoblastoma and germ-cell tumor. The older the onset age after puberty, the higher the malignancy risk is. Once diagnosed, bilateral gonads should be excised as soon as possible.