Background. – Mucopolysaccharidosis I (MPS-I) is an autosomal recessive disorder, which is caused by mutations in the IDUA gene. It induces the deficiency of glycosidase α-L-duronidase. The enzyme that is required for the degradation of heparan and dermatan sulfate. This disorder expresses a wide range of clinical symptoms (severe mental retardation, skeletal deformations, hepatosplenomegaly, corneal clouding and mild visceral organ involvement). In the present paper, we report the frequencies of haplotypes of the Eco47III–NspI sites, in the IDUA gene, in Mexican healthy and in MPS-I individuals. Methods. – Eco47III and NspI intragenic polymorphisms in IDUA gene were studied in 262 (524 chromosomes) Mexican healthy subjects and in 53 (106 chromosomes) MPS-I patients. Results. – The genotypes for IDUA Eco47III and NspI sites in Mexicans were in agreement with Hardy–Weinberg expectations. Allele frequency distributions for individual sites differed (P < 0.05) in both groups. Haplotype Eco47III–NspI frequencies of Mexican MPS-I patients also differed from those of the normal Mexican population. The data provide evidence of linkage disequilibrium, since the MPS-I group constitutes a subset of the Mexican control population. The disequilibrium in Mexican MPS-I patients was defined by an increase in the haplotype A1B2, and deficiency in A2B1, with respect to normal population (P < 0.05). Conclusions. – Our results support that these polymorphisms can be associated to mutations in IDUA gene, which leads to MPS-I in Mexican patients. On the other hand, these polymorphisms can be used to identify heterozygosity when they are informative.