The authors present an unusual case in which increased intracranial pressure developed because of multiple-suture craniosynostosis and megaloencephaly in a child with a previously undiagnosed lysosomal storage disease, alpha-D-mannosidase deficiency. This 3-year-old boy presented with a history of frequent naps, headaches, florid papilledema, enlarged head (> 95th percentile), elevated opening pressure by lumbar puncture, a "beaten copper" appearance on skull radiographs, and no hydrocephalus. Multiple synostectomies were performed. Postoperatively, the child's headaches and papilledema resolved and his level of physical activity increased dramatically. The authors discuss the paradoxical presentation of prematurely fused sutures and macrocrania in light of this lysosomal storage disease and its subsequent management.