We report on 45 fetuses with prenatally diagnosed bilateral cystic hygromata colli by ultrasound. Two of the 45 cases involved a twin pregnancy with only one fetus showing hygromata colli. In 2 cases there was only isolated hygromata colli. The other 43 cases showed the signs of non-immune hydrops fetalis. The cytogenetic findings were: 9 fetuses with Turner syndrome, 1 fetus with Turner mosaicism, 1 fetus with trisomy 18, 6 fetuses with trisomy 21, 12 fetuses with normal karyotype, and 16 fetuses with a failed chromosome culture. In fetuses with Turner syndrome and normal karyotype the sonographic findings were similar: massive bilateral hygromata colli, substantial fluid accumulations in skin and body cavities, oligohydramnios and intra-uterine growth retardation. In the cases with trisomy 21, the relative size of the hygromata colli was smaller. Intra-uterine growth retardation and oligohydramnios were not observed. The sole survivor of our group (elective pregnancy interruption: 30 cases; intra-uterine death: 14 cases) (karyotype: 46,XY) presented sonographically with massive ascites, a moderate cystic hygroma, and appropriate fetal development, and a normal amniotic fluid quantity. These findings are analysed in order to provide recommendations for prenatal diagnosis, prenatal management and genetic counselling of the couples concerned.