A rare case of sirenomelia with its autopsy findings is reported. The 1188 g infant was delivered by cesarean section at the 36th week of gestation, and died at 4 h of life. Physical and pathologic findings included sirenomelia (a single lower extremity mass), lung hypoplasia, bilateral renal agenesis, blind-ending colon, severe deformity of the bony pelvis, an imperforate anus, absence of the bladder, and a single umbilical artery. Because of the difficulty in determining the sex of the infant, PCR directed against the SRY gene was performed. The PCR-based sex determination is a rapid technique in patients with ambiguous genitalia.