Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant neurodegenerative disorder caused by the expansion of an unstable (CAG)_n repeat on chromosome 6p. We investigated 36 German families suffering from hereditary ataxias for the SCA1 mutation and elaborated clinical and neurophysiological characteristics. SCA1 accounts for 10 ‐ 15% of dominant cerebellar ataxias in German kindreds. The clinical presentation is characterized by broad, even intrafamilial variability and multiple system involvement already in early stages. Slowed saccades, ptosis and facial weakness are more prevalent in SCA1 but were unspecific differences compared to non‐SCAl ataxias. Two electrophysiological parameters characterize SCA1: markedly prolonged central motor conduction time in motor evoked potentials and predominantly demyelinating polyneuropathy. Molecular genetic analyses are indispensable to diagnose SCA patients precisely. Extensive neurophysiological studies are recommendable in the clinical approach as they are suitable to discover subclinical damage of the nervous system. In contrast to the enormous variability of clinical signs in SCA1 neurophysiological findings are rather constant.