Sirenomelia, also known as mermaid syndrome, is a rare congenital malformation in which the lower limbs fuse together, giving the appearance of a mermaid's tail. It is frequently combined with severe urogenital and gastrointestinal anomalies. We report the case of a 30-year-old pregnant woman. During this pregnancy, sirenomelia was first diagnosed during a routine 2nd-trimester ultrasound examination, which showed fusion of the lower limbs. Neither she or any member of her family had a history of diabetes. As for other risk factors, she had no history of exposure to teratogenic agents during her pregnancy. Moreover, her marriage was not consanguineous. Sirenomelia is a rare malformative sequence that should be diagnosed as early as possible. Bilateral renal agenesis, confirmed by color Doppler, makes it a lethal condition.