Summary. Objective. To evaluate the clinical, electro-encephalographic and evolutionary characteristics of a series of patients diagnosed as having benign neonatal sleep myoclonus (BNSM). Material and methods. The clinical histories of 21 patients with BNSM were analyzed. Criteria for inclusion in the study were: neonates who had had more than one episode of myoclonia during sleep and in whom neurological examination and psychomotor development were normal. Criteria for exclusion: Patients with myoclonia whilist awake, a perinatal history which included significant pathology and/or the diagnosis of epilepsy. The period of evolution varied from 6 months to 5 years, and the following parameters were considered: clinical features of the myoclonia, neurological examination, pychomotor development and evolution. EEG were done between crises in all patients. In 5 cases we recorded EEG during crises and in 2 cases video-EEG were done. Results. The study group was made up of 11 girls and 10 boys. The myoclonia started between the first and twenty third day of age (average = 7 days). Fifteen (71.4%) of the patients had generalized myoclonia, mainly in the distal part of the upper limbs in 13 and in the lower limbs in two. In 20 cases (95.2%) jerking was of short duration, lasting 10 to 20 seconds. In one case, the jerks were repeated in series lasting 30 minutes. Two patients later developed benign myoclonia of early infancy. The myoclonia disappeared before the age of 7 months in all cases. Conclusions. BNSM is seen in healthy newborns and disappear spontaneously during the first months of live. Differential diagnosis whit epileptic seizures is imperative in order to avoid unnecessary medication [REV NEUROL 1998; 26: 540-4]. Key words. Differential diagnosis. Neonatal myoclonia. Sleep.