Mucopolysaccharidoses (MPS) are a group of lysosomal storage disorder caused by accumulation of glycosaminoglycans (GAGs). MPS II is the most common subtype of MPS, and 70% of MPS II is severe type in Korea. We evaluated cognitive and developmental status, daily activities and caregiver-assistance in children with severe type of MPS II and MPS III. We assessed a total of 19 patients diagnosed with MPS II (17) and III (2). We selected tools according to guidelines for obtaining accurate test scores specifically in low-functioning and behaviorally disruptive pediatric patients. (1) using disease-specific protocols to assess salient aspects of the known phenotype, (2) selecting appropriate tests, (3) managing behavior, and (4) using age-equivalent scores on standardized tools. Bayley Scales of Infant Development-III (BSID-II) was used in children with MPS under 3 years, and Kaufman Assessment Battery for Children-II (KABC-II) was used over the age of 3 years. Vineland Adaptive Behavior Scales-II (parent-reported age-equivalent scores) was used to check adaptive function besides cognitive ability in all ages. In addition, the Pediatric Evaluation of Disability Inventory-Computer Adaptive Test (PEDI-CAT) was performed because it is feasible tool to measure the functional independence such as social function, self-care, and mobility of children from birth to 20 years of age. We investigated validity of the PEDI-CAT against Pediatric Evaluation of Disability Inventory (PEDI) and MPS Health Assessment Questionnaire (MPS-HAQ). We tested and retest PEDI-CAT to evaluate reliability of this test The median age at evaluation was 5.7 years ( 2.3 - 17.7 years). All patients were male. Eleven patients revealed floor scores due to behavioral problems. Therefore, we also tried to perform Visual Motor Integration (Beery VMI-6), and got the scores which were very low level in integrating or coordinating visual perceptual and motor. Six patients showed mild to moderate intellectual disability on KABC-II, and one patient showed delayed development on BSID-III. PED-CAT, PEDI and MPS HAQ showed good correlation. It is necessary to collect long-term data every year in a larger number of MPS patients with neurodegeneration. This approach will enhance the assessment of disease progression and monitoring of treatment outcome in future clinical trials for neuropathic MPS.