Several disorders of oxidative metabolism have been described in association with subacute necrotizing encephalomyelopathy (SNE) or Leigh syndrome. We present an eight-year-old girl with a mild spastic paraparesis and clinical deterioration on intercurrent infections. One sib died of SNE proven by autopsy. Biochemical examination of muscle tissue points to a disturbance in the process of oxidative phosphorylation due to a disturbed oxidation of NADH. The biochemical disorders associated with SNE are reviewed. The relation of SNE to the concepts of encephalomyopathy and mitochondriopathy is discussed.