An autopsy case of infantile osteopetrosis complicating neuronal ceroid-lipofuscinosis is reported. Autopsy revealed generalized sclerosis and thickening of cortical and spongy bones, formation of mineralized cartilagenous tissues, and narrowing of the marrow cavities associated with decreased hematopoietic cell components. Around the thickened bone trabecles, osteoclasts lacked a ruffled border and clear zone along the cell membrane facing the bone matrix surface. The brain was markedly atrophic with neuronal cell loss and focal gliosis, and the remaining neuronal cells accumulated brown granular pigments, which were confirmed histochemically and electron-microscopically to be ceroid and lipofuscin. In the cerebral medulla, the development of myelin sheaths was extremely poor. Also, the occurrence of Lex type glycolipids and GM3 and the apparent absence of cerebroside and cerebroside sulfate were proved by biochemical analysis, suggesting that the brain was still in a stage of embryonic development or still in the process of differentiation. Except for one suggestive case, this is the first case of complicating neuronal ceroid-lipofuscinosis in infantile osteopetrosis.