Neuropsychological assessment is essential in providing documentation of the untreated natural history of storage diseases associated with dementia and quantifying the effectiveness of treatment on central nervous system function. Baseline characterization and outcome of bone marrow transplantation (BMT) for three leukodystrophies and three mucopolysaccharidoses are presented. Results suggests that BMT for Hurler syndrome, adrenoleukodystrophy, and globoid cell leukodystrophy can be effective in preventing dementia if done early enough in the disease. Sanfilippo and Hunter syndromes do not benefit and BMT is not recommended. For metachromatic leukodystrophy, BMT is not recommended for symptomatic early-onset forms of the disease. Further longitudinal follow-up is needed to determine whether the benefits outweigh the risks of BMT for late-onset and preclinical metachromatic leukodystrophy.