A 25-year-old man developed nausea, vomiting, severe headache, and confusion. He had a past history of hyperuricemia and mild renal dysfunction. On admission he had somatic growth retardation, hypertrichosis, and bilateral auditory impairment. A cranial CT scan showed a small area of low density in the left temporal lobe and cerebellar atrophy. Five days later, he developed right homonymous hemianopia, sensory aphasia, and sensory inattention, and a new, large area of low density in the left occipital lobe on a cranial CT scan. On laboratory examination, lactate, pyruvate, and the lactate-to-pyruvate ratio were elevated in both the serum and cerebrospinal fluid. The biopsied muscle showed ragged red fibers and strongly SDH-reactive blood vessels. Gene analysis revealed the presence of the A 3243 G point mutation of the mitochondrial tRNA(Leu) gene in his blood leucocytes and muscle. Serum concentrations of BUN and creatinine were elevated to 46 mg/dl and 2.2 mg/dl, respectively. Creatinine clearance was 14.1 ml/min. An abdominal CT scan disclosed atrophy of his left kidney with subcapsular calcification and the findings of his abdominal ultrasonography were compatible with chronic renal failure. His mother, who suffered from renal failure and became dialysis dependent in her late forties also bore the A 3243 G mutation of the mitochondrial tRNA(Leu) gene in her circulating leucocytes. Though the association between MELAS and renal dysfunction still remains obscure, we speculate that renal failure can be a manifestation of MELAS.