We describe a case in which the typical ultrasound diagnosis of infantile polycystic kidney in a woman with no family history of renal disease was not confirmed by histology following termination of the pregnancy. This is contrasted with the situation in another couple who were known carriers of autosomal recessive polycystic kidney disease and where the prenatal ultrasound diagnosis was confirmed histologically. When prior genetic risk is low, the possibility of a normal or less severe outcome must be discussed with parents when fetal ultrasound shows large, echogenic kidneys but normal amniotic fluid volume.