There are two forms of gonadal dysgenesis - mixed and pure. In the mixed form, some differentiated gonads as well as some either ovarian or testicular rudiments are present. This form results in a number of phenotypes with a possibility of malignant transformation. In the pure form occurring in female gender, also some rudimental gonads are bilaterally present. In the case of simultaneous presence of Y chromosome, also some malignant transformation may appear (Siklar et al. 2007). Chromosomal aberrations are present in 2-7 % adult pairs with fertility disorders and in 0.6 % of newborns. However, only few cases with similar chromosomal aberrations were described so far (Roubin et al. 1977; Alexander et al. 1978; Teyssier et al. 1982; Caglayan et al. 2009). Mixed gonadal dysgenesis presents as a unilateral testis, usually intraabdominal, also with a streak gonad on contralateral side, and persistent mullerian structures. 45X/45XY karyotype is the most frequent in such cases with predominance of 45X cells in both peripheral lymphocytes and gonads. We present a rare case of a left undescended testis, normally descended right testis, with penoscrotal hypospadias, who had a normal karyotype and whose histopathological findings were endometrial tissue and fallopian tube in left testicular biopsy. Gonadal dysgenesis should always be kept in mind because of a possibility of undescended testis and proximal hypospadias. If karyotype reveals a 46XY gonadal dysgenesis, these patients need the careful follow-up to screen for gonadoblastoma in remaining normal testis. Subjecting the patients to prophylactic orchidectomy with hormone replacement can be an additional option in such patients.