A 60-year-old woman had developed ptosis, progressive external ophthalmoplegia and action tremor over the last ten years. Physical examination also revealed short stature and retinal pigmentation. Anaerobic forearm exercise test showed increase of basal lactate and rise of lactate/piruvate index. Biceps biopsy displayed numerous ragged red fibers. Respiratory chain studies were consistent with complex I deficiency. Point mutations or deletions in mitochondrial DNA were not found. MR identified a diffuse leukoencephalopathy over both cerebral hemispheres, mesencephalon, pons and cerebellum. The late and sporadic onset of a progressive external ophthalmoplegia outlining a Kearns-Sayre syndrome is striking. A leukoencephalopathy associated with mitochondrial encephalomyopathy is an infrequent finding. The action tremor of this patient could be symptomatic of her mitochondrial disfunction.