Purpose To further characterize the mutations within the CHST6 gene responsible for causing macular corneal dystrophy in a cohort of affected patients from the United States. Design Experimental study. Methods Genomic DNA was extracted from buccal epithelium of 16 affected patients (14 families), 17 unaffected relatives, and 127 controls, followed by polymerase chain reaction amplification and direct sequencing of the CHST6 coding region. Subtyping of affected patients into type I and II macular corneal dystrophy was performed by measuring antigenic keratan sulfate (AgKS) serum levels. Haplotype analysis was performed in families that demonstrated common mutations. Results CHST6 coding region analysis in 10 patients identified as having type I macular corneal dystrophy revealed 10 sequence changes: eight missense mutations, four of which are novel (Met104Val, Tyr110Cys, Gln122Pro, and Leu276Pro) and four of which have been reported previously (Ser51Leu, Pro72Ser, Cys102Gly, and Leu200Arg); one novel homozygous nonsense mutation in two patients from a single family (c. 1683C>T, Gln331X); and one frameshift mutation in a heterozygous state in a single patient (c.1744_1751dupGTGCGCTG). Mutation analysis in the four patients identified as having type II macular corneal dystrophy (serum samples were not obtained from two affected patients) revealed three patients heterozygous for either the c.923G>C, c.969C>A, or c.1519T>C sequence changes. The fourth patient was compound heterozygous for c.969C>A and c.1291T>G. None of these changes was observed in 127 control individuals. Haplotype analysis using microsatellite markers flanking the CHST6 gene did not reveal a common founder for the Leu200Arg (1291T>G) missense mutation, present in five families, identifying this position as a mutation hot-spot. Conclusions A variety of previously unreported mutations in the coding region of the CHST6 gene are associated with type I macular corneal dystrophy in a cohort of patients from the United States.