Background: The category of lysosomal storage diseases known as mucopolysaccharidoses (MPS) is characterized by the buildup of glycosaminoglycans (GAGs) in tissues and organs as a result of the lack of certain enzymes needed for the breakdown of cellular GAGs. For all individuals, the Wechsler and Primary Scale of Intelligence (WPPSI) was used to calculate their intelligence quotient (IQ) and evaluate their cognitive abilities. Objective: The aim of the present study was to assess intelligence quotient in MPS children. Patients and Methods: This study was conducted in 72 children in Pediatrics Department in Zagazig University Hospital, over 6 months. They were divided into 2 groups; A case group included 24 children diagnosed with MPS in Pediatrics Department in Zagazig University Hospital, and a control group included 48 children matched for age and sex. Results: This study showed that age of onset of disease ranged between 1 and 6 with mean 1.96 (SD 1.30) years. This study showed that the mean age of diagnosis was 5.25 (SD 2.83) years and ranged between 1 and 13. The present study showed that all cases with MPS had positive coarse facies. The mean value of full IQ was statistically lower among the case group than the control group. Conclusion: Among children with MPS, there was a measurable decrease in IQ associated with positive family history. IQ was low among children with MPS compared with controls.