This report is made to emphasize the care needed to separate cases of macrocephalus due to diffuse degeneration of the brain from those due to hydrocephalus or tumor, with which they might become confused. REPORT OF CASE History. —A white male child, born in Roxbury, Mass., was first seen in the outpatient department when 10 weeks of age. The complaints were: vomiting, constipation and failure to gain weight. There were a discharge from the nose, redness of the left ear drum and a slight rachitic rosary over the ribs. Nothing, however, was known of the birth history or early development. At 9 months, he was again brought to the outpatient department, when it was noted that the anterior fontanel was tense, and that there was a fine vertical nystagmus, a weak action of the left external rectus and a dull note on percussion of the head, which measured 171/4 inches