A 59-year-old man with hypertension and severe renal dysfunction was diagnosed as having adult glomerulocystic kidney disease. MR imaging of the kidney showed a diffuse reduction of the intensity of the renal cortex with a loss of normal cortico-medullary differentiation on T1-weighted images. Numerous small cortical cysts were also demonstrated. These MR findings complemented the results of the biopsy and were useful for making a definitive diagnosis.