We report renal lesions and functional alterations in a 32-year-old man with Fabry's disease (ceramidetrihexosidase deficiency). By light microscopy of a renal biopsy specimen, distinctive "foamy" cytoplasmic alterations were observed in renal glomerular, tubular, vascular, and interstitial cells. Histochemical analysis of vacuolated epithelial cells showed glycolipid- and phospholipid-like material. Ultrastructurally, dense osmiophilic as well as stacked and concentric laminated profiles were observed within these epithelial cells. In addition, glomerular endocapillary, parietal, and vascular epithelial cells contained opaque osmiophilic granular deposits with paracrystalline arrays. Renal function studies indicated a glomerular filtration rate of 86.1 mL/min/1.73 sq m, effective renal plasma flow of 415 mL/min/1.73 sq m, tubular reabsorption of glucose of 356 mg/min/100 glomerular filtration rate, and maximal urinary concentrating and diluting ability of 568 and 46 mOsm/kg, respectively. Serum ceramide hexosidase activity was 0.18 nmole/hr/mL (normal, 8 to 15). We conclude that renal dysfunction associated with Fabry's disease is associated mainly with accumulation of glycolipid and phospholipid compounds in the walls of blood vessels and distal nephrons.