Subacute progressive panencephalitis is usually a progressive and fatal disease, being uncommon temporary or definitive remissions. A three years old boy, previously vaccinated against measles, developed trembling, progressive and severe mental deterioration, partial seizures and myoclonic jerks. The electroencephalogram showed periodic high amplitude waves concomitantly with myoclonic jerks and the cerebrospinal fluid revealed an increase of the gammaglobulin fraction (16,8), benjoin coloidal reaction shifted to the left and the antimeasles antibody titres were positive (complement fixation text 1:16; neutralization test 1:32). In spite of that, two months after the beginning of the illness the patient showed mental and motor improvement and similar modifications of the electroencephalographic aspects and now, eleven months later, is well, remaining only a slight motor and mental deficiency.