A disorder of sex development (DSD) is defined as a congenital condition in which development of chromosomal, gonadal, or anatomical sex is atypical. Swyer syndrome is an example of 46,XY DSD with a female phenotype. It usually becomes apparent in adolescence with delayed puberty and amenorrhoea. Spontaneous breast development is very rare. A 15-year-old girl was presented due to primary amenorrhoea with breast development compatible with Tanner stage V. Hormonal tests revealed hypergonadotropic hypogonadism with low level of oestradiol. Pelvic ultrasound and magnetic resonance imaging revealed a small uterus, and no ovaries were found. In the right lower abdomen, a structure of unknown origin was visible. The chromosome analysis revealed a 46,XY karyotype. The patient was qualified for a laparoscopic bilateral gonadectomy. Postoperative histopathological examination revealed gonadoblastoma. We underline the need to consider DSD 46,XY in the presence of primary amenorrhoea, even when pubertal development is present. Germ cell tumors have a tendency to grow and metastasize rapidly. Delayed diagnosis may increase the risk of malignant transformation and cause a poor diagnosis.