Mutations in the MCOLN1 gene cause mucolipidosis type IV (MLIV), a severely debilitating, autosomal recessive, lysosomal storage disorder. Approximately 80% of patients with MLIV are of Ashkenazi Jewish (AJ) descent, and two mutations, IVS3-2A-->G and 511del6434, account for >95% of the mutant alleles in this population. To determine the carrier frequencies of these two mutations, 2,029 anonymous, unrelated, unaffected AJ individuals from the greater New York metropolitan area were screened. A multiplex PCR method coupled with allele-specific oligonucleotide hybridization was developed, to enable large-scale screening. The frequencies of the IVS3-2A-->G and 511del6434 mutations were 0.54% and 0.25%, respectively, for a combined carrier frequency of 0.79%, or 1 in 127 individuals (95% CI 0.40%-1.17%). The addition of both AJ mutations causing this neurodegenerative disorder should be considered for prenatal carrier screening in this population.