The authors describe the electroclinical aspects and evolution of nine cases of myoclonic epileptic encephalopathy which began between two days and ten weeks of life. At onset it is associated with: myoclonic jerks, partial fits and periodic paroxysmal EEG abnormalities. Repeated spasms coexisting with partial fits and 'suppression-bursts' (both appearing later) complete the electroclinical picture. The neurological status (initially normal) progressively deteriorates leading within a few months to a decerebrate posture with opisthotonos. In spite of thorough neuroradiological, biochemical, cytological, metabolic, and ultrastructural investigations, the etiology remained unknown. However, the electroclinical and evolutive patterns are similar to those of some metabolic diseases (Polyodystrophy, Non-Ketotic Hyperglycinemia, etc.). All these observations display a homogeneous electroclinical pattern for which the authors propose the name of Early Myoclonic Epileptic Encephalopathy. This type deserves to be classified as a particular electroclinical entity among the epileptic encephalopathies of the first year of life; since its course is regularly downhill in all cases there may be a familial recurrence due to the possibility of a metabolic etiology.