The last decade has seen great changes in the diagnosis of inherited ataxias. Previously mysterious diseases are now recognized to be caused by specific mutations for which genetic screening is readily available. In many cases, the discovery of the molecular basis has broadened the definition of possible clinical manifestations of particular inherited ataxias. The type of mutation underlying the more common forms of inherited ataxia-unstable trinucleotide repeat expansions-helps to explain some of the unusual features of these diseases. This article reviews recent genetic advances in ataxia. The aim is not to present an exhaustive summary but rather to provide guidance in evaluating ataxia, particularly with respect to recent molecular genetic findings.