The molecular defect in fascioscapulohumeral muscular dystrophy (FSHD) has proved difficult to explain. Although contraction within a polymorphic tandem repeat located at 4q35.2 is unequivocally associated with disease expression, the specific biological mechanism involved in the phenotype has yet to be resolved. Several studies have demonstrated that a specific 4q35.2-located haplotype (4qA161) is also closely associated with FSHD expression. Therefore, in this study we analyzed the haplotype association in a large cohort of sporadic and familial FSHD families from the UK. In all cases the affected individuals displayed the 4qA161 haplotype.