Little information is available concerning hereditary renal disease in the Irish population. We studied the prevalence and types of hereditary renal disease that lead to end stage renal failure by looking at the underlying hereditary disease in our dialysis populations and in all patients transplanted at the national unit. Twenty eight (15.7%) of 178 dialysis patients had hereditary renal disease with a mean age of 31 years (range nine to 65), and a male to female ratio of 1.54:1. Eighty-nine of 842 patients (10.3%) with renal transplants had hereditary renal disease with a male to female ratio of 1.63:1. The commonest entity was autosomal dominant polycystic kidney disease (68% in dialysis patients, 64% in transplants), and the next most frequent was Alport's syndrome (21.4%, 16.9%). Nephronophthisis was the third most common problem (10.7%, 10.1%) followed by hereditary non-Alport's nephritis, Fabry's disease, cystinosis and familial interstitial nephritis. The high prevalence of hereditary renal disease among the dialysis and renal transplant population emphasises the need for proper registration of the nature of renal disease in this group, and for a comprehensive genetic counselling service in this country.