The clinical features and laboratory data of 93 children with polycystic kidney disease were analysed. Family studies showed that the disease was dominant (DPKD) in 17 and recessive (RPKD) in 32 of them. Of the remaining 44 sporadic patients, 1 was classified by histological and/or imaging findings as having DPKD, 41 as having RPKD and 2 could not be classified. The symptoms tended to be more severe in RPKD than in DPKD, but there was much overlap. Death in early life was common in RPKD (55/73) and more rare in DPKD (4/18). If a child with DPKD had disease manifest during the neonatal period, then siblings were usually affected in the neonatal period. Survival to adulthood was seen in both diseases. In the patients who survived the neonatal period, hypertension was more common in RPKD (11/18) than in DPKD (4/14). Symptoms of portal hypertension were present in 2 patients with RPKD and none with DPKD. None of the laboratory investigations discriminated between the two entities. Glomerular filtration rate was diminished more often in RPKD (9/11) than in DPKD (2/8). Some difference was seen in the maximal urine concentrating ability; it was always reduced, often markedly, in RPKD but usually either normal or only moderately disturbed in DPKD. Studies on hepatic function and hepato-cellular damage were usually normal, but bacterial cholangitis was noted in some children with RPKD. The differential diagnosis between DPKD and RPKD needs to be based on the family history, family studies, radiological and/or histological features.