Seven hundred children referred to the clinic for mental retardation were screened for various inborn errors of metabolism. Eighteen were found to have mucopolysaccharidoses (MPS). Ten of these children were followed for a period of five years. Three of them died. Two of them had type 1 MPS, based on physical findings, biochemical investigations and deficient iduronidase activities of leucocytes. There were seven patients with MPS type II in this series. Two pairs were siblings. Skin cultures carried out in Dr Neufeld's Laboratory showed iduronate sulphatase deficiency. Three patients had type IV mucopolysaccharidoses. Two were siblings. In one patient leucocyte beta-galactosidase activity was about 1/8th of normal control. One patient had MPS type VI; her leucocytes had no detectable aryl sulfatase B. One patient had unclassifiable MPS. They had some clinical improvement as a result of parental care but the progression of the disease has remained unaffected.