We present a family in which the first affected child presented with a 'milder' form of the hydrolethalus syndrome and survived to seven months, and two subsequent pregnancies with typical features detected early by ultrasound evaluation. We propose that the 'milder' cases are indeed true cases of the hydrolethalus syndrome and that allelic variability may be responsible for these 'non-typically Finnish' findings. We also demonstrate that, especially in families where there has been a previously affected fetus, echographic diagnosis can be made in the first trimester, as early as the 11th week of gestation.