Spinocerebellar ataxias (SCAs) are a group of clinically and genetically heterogeneous neurological diseases. The expansion of unstable microsatellite repeats has been identified as the underlying pathogenic cause of 10 subtypes of autosomal dominant SCAs. The aetiology of sporadic SCA is unknown. The aim of this study was to investigate the effect of large normal repeats in patients presenting with sporadic or familial ataxia compared to a control population. The size of the expansion was determined using a fluorescent PCR approach in 10 common SCA genes: SCA-1 (ATXN1), SCA-2 (ATXN2), SCA-3 (ATXN3), SCA-6 (CACNA1A), SCA-7 (ATXN7), SCA-8 (ATXN8OS), SCA-10 (ATXN10), SCA-12 (PPP2R2B), SCA-17 (TBP) and DRPLA (ATN1), in 165 ataxia patients and 307 controls of Welsh origin. There was no difference between cases and controls in the distribution of the large normal alleles, or in the distribution of the combined CAG repeats. The normal allele distribution in the Welsh population was largely similar to that of other Caucasian populations. Our study failed to demonstrate an effect of large normal repeats on the susceptibility to develop ataxia.