The spinocerebellar ataxias (SCAs) with autosomal dominant inheritance are a clinically and genetically heterogeneous group of neurodegenerative disorders. To date 27 different loci have been identified for these conditions. Recently, two deletions as well as one missense mutation in the beta-III spectrin gene (STBN2) were identified causing SCA5. To evaluate the clinical relevance of these mutations, we screened 310 familial and sporadic patients with ataxia. While none of the individuals tested had evidence for one of the known SCA5 mutations, additional sequencing of the coding region for 22 unrelated patients revealed three novel missense exchanges at evolutionary conserved amino acid positions. Even though each variation marks a unique genotype in 250 alleles, a disease causing capacity can be excluded with high probability. These results reflect the challenges for molecular analyses in SCA5.