A case of membranous lipodystrophy complicated by Fanconi's syndrome is described. A 40-year old man complaining of pain in his legs was admitted to our hospital. Roentgenograms showed cystic changes in the long bones. Biopsy of the affected lesion of the femur revealed a peculiar membranocystic structure in the marrow that is typical of membranous lipodystrophy. He had a neuropsychiatric disorder which is often associated with this disease. Laboratory studies were remarkable for renal proximal tubular dysfunction, i.e., Fanconi's syndrome. Membranous lipodystrophy is a rare, hereditary disease that has been reported mainly from Japan and Finland. This is the first case of this disease complicated by Fanconi's syndrome. The possible relationship between these disorders is discussed.