A rare case of infantile myasthenia gravis (congenital type) is reported. The child was 16 months old at the time of the diagnosis, although she presented signs suggestive of the disease since two months earlier. The diagnosis was based solely upon clinical criteria, including immediate response to a therapeutic test with Neostigmine, followed by excellent response to treatment with Mestinon. A review of the different types of myasthenia gravis in infancy is made, with emphasis on the clinical criteria for differential diagnosis of these cases.