Ammonium urate urinary stone: its surface structure and incidence in Japan.

We report on a middle-aged woman with a stone in the right kidney, derived from ammonium urate. Its surface structure was examined by scanning electron microscopy. Ammonium urate is a very rare component of urinary stones in industrialized countries, and they are thought to have an incidence of lower than 0.1% in Japan. The aetiology of ammonium urate-derived stones was investigated from an endemo-epidemiological viewpoint.