An 8-year old boy with genetically confirmed X-linked myotubular myopathy developed progressively worsening dementia and subclinical seizures at age 5-6 years. Previously, seizures or dementia have been noted in only a small number of myotubular myopathy patients, and only in association with significant metabolic disturbances. This patient had no evidence of hypoxemia or other metabolic disturbance. The present case suggests that the clinical spectrum of X-linked myotubular myopathy is broader than previously considered and may include mutation-dependent central nervous system disease.