This paper about cystinosis is focused primarily on nosology and genetic heterogeneity, the recurrent themes of these conferences. It briefly discusses cystinosis in relation to other disorders which cause the renal Fanconi syndrome with or without glomerular insufficiency, points out the methods for its reliable diagnosis, and then summarizes evidence suggesting that cystinosis should be classified as one of the lysosomal storage diseases. More extensive reviews of cystinosis are available.