Glomerulocystic kidney characterized by dilatation of Bowman's space occurs primarily in infants and children. We treated a normally developed 29-year-old Japanese man for hypertension and renal failure, who had been well up to 6 months before admission. Extrarenal malformations were not determined. A biopsy of both kidneys was done at the time of interdialysis, and the histology revealed diffuse glomerular cystic lesions. Electron-dense deposits were also observed in the mesangial area. Radiological studies of the kidneys showed numerous minute cysts in the cortical area, a normal architecture of the arterial trees, and negative evidence of urinary tract obstruction. This may be the first documentation of glomerulocystic kidney in an adult, without extrarenal anomalies.