A refined genetic map of the spinocerebellar ataxia 2 locus was constructed through linkage and haplotype analysis of 11 large pedigrees from the Holguín SCA2 family collective. Three-point analysis makes a localization of the SCA2 mutation in the 6-cM interval D12S84-D12S79 likely. This is consistent with haplotype results indicating a crossover event between two branches of the SCA2 family Rs and placing the mutation on the telomeric side of D12S84. The microsatellite D12S105 within this interval shows a peak two-point lod score of Z = 16.14 at theta = 0.00 recombination and complete linkage disequilibrium among affected individuals. These data together with the observation of a common disease haplotype among all family ancestors support the notion of an SCA2 founder effect in Holguín province.