Polycystic kidney disease was investigated in 28 families in which at least one member attended the paediatric nephrology clinic at a Johannesburg or Pretoria hospital. Twenty-five (89.3%) of the families had autosomal recessive polycystic kidney disease (ARPKD), and of these a significantly larger number than would have been expected (92%) were Afrikaans-speaking. There was a consanguineous marriage in the ancestry of 2 patients but 6 of the families (26%) had ancestors with one surname in common and 7 of the families (28%) had their origin in the western Transvaal. A point prevalence for ARPKD of 1:26,000 was estimated for the Afrikaans population (based on the age cohort 0 - 19 years) and the carrier rate for the gene was 1:83; on the basis of the live-birth rate for ARPKD of 1:11,000 the carrier rate is 1:53. These findings suggest that ARPKD may be unusually frequent in the Afrikaans-speaking population. A founder effect is probably responsible.