Three patients with primary megalencephaly were identified among 40 children seen in our clinic with pseudopapilledema due to optic disc drusen. These patients were genetically unrelated and did not have cutaneous hemangiomas, distinguishing their condition from the Riley-Smith syndrome. Although the nature of the relationship between optic disc drusen and primary megalencephaly is not clear, we feel that the two conditions have more than a chance association. A clinically important consideration is that the concomitant occurrence of pseudopapilledema due to optic disc drusen and a large head due to primary megalencephaly may lead to an erroneous diagnosis of increased intracranial pressure in children.