Progressive external ophthalmoplegia with ptosis was found to be associated with retinal pigmentary changes of various degrees in six patients. Recessive inheritance was suggested in one case. Electromyography of the extraocular muscles showed an interference pattern contrasting with the marked paresis. A strabismus divergens was successfully treated surgically in two patients. Histologic and electron microscopic investigation of extraocular muscles revealed extensive disintegration and destruction of myofibrils combined with marked changes in mitochondria, whereas intramuscular nerve axons appeared unaffected. There was additional histological or myographical evidence for involvement of skeletal muscles in three patients. Muscle specific serum enzymes were generally increased. Neurological symptoms indicating a cerebral disease were missing. The concluding diagnosis, ocular myopathy, was based upon the composite pattern revealed by the diagnostic procedure, but primarily upon the ultramicroscopical findings in extraocular muscles.