SUMMARY The sirenomelia is a strange congenital malformation characterized by fused lower limbs, associated with other visceral abnormalities, which are incompatible with life in the vast majority of cases. Its etiology is not clear until now. Its prevalence is reported among 1 and 2 in 100,000 births. In this paper 4 sirenomelia cases of newborn at Valle University Hospital in Cali, Colombia between December 9, 2004 and February 2, 2005, which would correspond to a prevalence of 3.5 cases per 1000 births for the search time, are presented.