Glomerulocystic kidneys can be categorized into three major groups: (1) glomerulocystic kidney disease, comprising nonsyndromal heritable and sporadic forms of severely cystic kidneys in children and adults, (2) glomerulocystic kidneys in heritable malformation syndromes, and (3) glomerular cysts in dysplastic kidneys. The first category includes diffusely glomerulocystic kidneys in newborns and young children, many of whom have family histories positive for classical polycystic kidney disease. No differences between familial and sporadic cases have been identified, apart from the family histories. The sporadic cases are conceivably new mutations of the same disease. The first category also includes sporadic and familial disease in older children and adults. The inheritance in adult familial disease, as in childhood familial disease, has been dominant. An apparently distinct entity is hypoplastic glomerulocystic kidney disease, a dominant reported in only a few families. These kidneys, apart from being glomerulocystic, are small, and imaging studies show abnormal pyelocaliceal anatomy. The second category includes glomerulocystic kidneys as major components of heritable syndromes such as tuberous sclerosis, orofaciodigital syndrome, brachymesomelia-renal syndrome, trisomy 13, and the short rib-polydactyly syndromes. The category also includes glomerular cysts in several syndromes, namely Jeune syndrome and familial juvenile nephronophthisis, better known for chronic progressive tubulointerstitial disease. Glomerular cysts occur as a minor component, i.e., scattered cortical cysts, in several other syndromes, among them Zellweger's, in which the cysts are typically present and are usually inconsequential, only occasionally serious enough to affect renal function. In all of these syndromes, the cysts are inconsistently expressed.(ABSTRACT TRUNCATED AT 250 WORDS)