A 22-year-old man with subacute necrotizing-encephalomyelopathy (SNE; Leigh's disease) was diagnosed as having progressive renal dysfunction. The clinical diagnosis of Leigh's disease was obtained by the typical central nervous lesions, abnormalities in other organs, and increased lactate concentrations in blood and cerebrospinal fluid. We performed an open biopsy of the right kidney. Light microscopic studies of the renal specimen showed diffuse glomerulocystic kidney (GCK) with tubulointerstitial damage. Electron microscopic examination showed marked swelling and increase in the number of mitochondria of the renal tubular epithelial cells. Therefore, it is suggested that mitochondrial disease seems to play an important role in developing GCK.