Growing skull fracture (GSF), also known as leptomeningeal cyst, is a rare but significant complication of pediatric head injury. It is mainly seen in infancy and childhood. GSFs of the posterior fossa are uncommon, and intradiploic location in the posterior fossa is extremely rare. Only a few cases of pediatric GSF of the posterior fossa and intradiploic location have been reported in the literature. We report a case of a 15-year-old boy who had large intradiploic GSF of the posterior fossa, associated with cervical syringomyelia. The lesion developed progressively over a period of 5 years following a documented occipital linear fracture. This case of a GSF developing from a known occipital linear fracture demonstrates that a GSF may reach a considerable size, and although uncommon, intradiploic development and occipital localization of a GSF are possible. Syringomyelia associated with posterior fossa GSF is very unusual which makes this case even more unique.