Nineteen hospitalized adult patients with progressive myoclonus epilepsy were studied. According to their clinical status they were divided into three groups of severity. The ages and duration of the disease did not differ significantly between the groups. The groups showed significant differences in ability of daily living, amount of spontaneous myoclonus, IQ and psychomotor reaction time. In EEG the groups differed in respect to the dominant occipital rhythm and amount of myoclonic spikes but not in respect to universal paroxysms. Myoclonic spikes and paroxysms in EEG were only loosely related. The results yield a conclusion that the deterioration caused by the disease is individual and the progression may even cease. In this respect progressive myoclonus epilepsy differs clearly from many hereditary neurometabolic and storage diseases.