Introduction/Background Gonadal dysgenesis belongs to the rare congenital abnormalities, affected patients are at increased risk of various types of germline tumors. Symptoms of dysgenetic ovarian tumors are not specific and are usually revealed not earlier then in puberty but it is often already in stage of advanced tumor.

Methodology A 13 year old girl was admitted to the hospital for suspicious diabetes insipidus, that was not proved. This patient had family history with report of her aunt who at the age of 17 underwent bilateral adnexectomy because of the dysgerminoma and gonadoblastoma of the ovaries followed by chemotherapy and subsequent HRT.

This girl was eunuchoid appearance with primary amenorea, Tanner’s clasification M IV, P IV (sparse), A 0. On the ultrasound there was small uterus with low endometrium and right ovary with oval solid mass 2 × 1.5 cm. The hormonal profile proved high values of FSH, the karyotype was 46 XY. The findings indicated laparoscopic gonadectomy.

Results Bilateral ovarectomy was performed and the histopathologic examination proved gonadoblastoma present in both ovaries. There were also signs of tumor transformation into the dysgerminoma in the right ovary. TNM classification was T1a Nx M0, FIGO IA. All findings corresponded to the diagnosis of Swyer’s syndrome. The hormonal replacement treatment and regular check up were suggested.

Conclusion Gonadal dysgenesis is not a frequent congenital defect and its transfer into the next generations is rather rare. The proper diagnosis is often difficult and it is based mainly on clinical symptoms. The late onset of puberty may be one of the first symptoms of the disease. The early diagnosis may prevent the transformation of the dysgenetic ovaries into the malignant tumors. The girls before the age of 15 should be therefore regulary examined by pediatrician with a careful evaluation of the signs of puberty.

Disclosure Nothing to disclose.