Sirenomelia, characterized by a fusion of lower limb buds, is rare. Moreover, the coexistence of this malformation with a VACTERL sequence is exceptional. We report, here, three new observations associating these two diseases on fetuses from 14 to 26 weeks gestation. With these three new cases associating sirenomelia and VACTERL, observed in our unit and examined in light of data from the medical literature, we discuss the embryologic origin of such malformations and the nosologic frontiers between these two diseases.