Intradiploic cysts are rare complications of skull fractures. Only five cases of cranial intradiploic cyst can be found in the literature, all affecting the occipital bone. In all, the primary injury occurred in childhood and the cyst presented many years later. The case described here is of a frontal intradiploic leptomeningeal cyst developing in an adult as a sequel to a skull injury 12 months earlier. Intradiploic cysts occurring after fractures in adulthood do not appear to have been described previously.