Sirenomelia, which is also known as mermaid syndrome and characterized by the fusion of the lower extremities, is the most severe form of caudal regression syndrome and one of the rare and lethal congenital malformations. The anomalies that might be seen in this syndrome include pelvic-sacral dysplasia, genital anomalies, bilateral pelvic renal fusion accompanied by renal dysplasia, colon atresia, unilateral umbilical artery, and imperforated anus. The incidence of sirenomelia is 0.8-1 cases in 60,000-100,000 deliveries and the male/female ratio is 2.7-3:1. The case reported in the present study was a 13-week-old male fetus 30 g in weight with a macerated appearance. The upper extremities had a relatively normal appearance but the lower extremities were conjoined and there was a single lower extremity consisting of conjoined feet and toes. In the face, the nasal bridge was sunken, the ears had a low position, and there were cleft palate and cleft lip. Examination of the external genital organs revealed that the penile part was in the anal region. There was no anus opening. The crown-rump length was 8.5cm, the heel-toe length was approx. 1cm, and the rump-heel length was approx. 3.7cm. There were none of the two kidneys, ureter, bladder, urethra, or rectum. In the umbilical cord, there were 2 venous structures, one of which was the artery. Perivillous congestion and hyperemia, perivillous calcification, deciduitis, and focal infarct regions were observed in placental tissues. This report aims to discuss this very rare case together with the literature.