A retrospective review of 199 black patients with urinary calculi and review of the census figures of the index hospitals revealed that white patients had urinary calculi 3 to 4 times as often as black subjects. The black male-to-female ratio was 1 to 1.55 compared to a ratio for white patients of 2.3 to 1. Calculi in black male subjects occur at a younger age than in black or white female or white male patients. The most common organisms cultured in black patients with stones were Escherichia coli and Proteus mirabilis. In contrast to the white population the most common type of stone formed in black patients was struvite/carbonate apatite. Stones of this type accounted for a third of all stones in male and 44 per cent in female subjects. We conclude that nephrolithiasis is an uncommon but not rare disease in the American black population.