Sirenomelia is a rare fetal malformation with more or less complete fusion of both lower limbs consistently associated with bilateral renal abnormalities. The positive diagnosis can be made antenatally by ultrasound during the first trimester of pregnancy but often before the 22 weeks of amenorrhea. The objective was to think about the possible diagnosis by ultrasound in front of the urinary anomalies and the ologiamnios during the morphological study of the second trimester of pregnancy. We report a case of sirenomelia in a 25-year-old lady as part of the routine prenatal assessment suspected and confirmed during the morphological ultrasound of the second trimester of pregnancy and confirmed after the termination of pregnancy in Mali in the Health Center of Reference of commune III of the district of Bamako. The morphological ultrasound made it possible to diagnose the malformation of the urinary tract, the amniotic fluid and to make the therapeutic decision of medical termination of pregnancy at the end of confirming the siren syndrome.