Ataxia disorders (or ataxias) include both hereditary and nonhereditary diseases of the cerebellum and spinal cord, all of which are clinically characterized by progressive ataxia. A distinction is made between ataxia disorders and focal diseases of the cerebellum (tumor, abscess, infarction, hemorrhage, demyelinating disease). Ataxias are classified according to the molecular causes, being divided into hereditary ataxias, sporadic degenerative ataxias, and acquired ataxias. The diagnostic tests to be applied should be selected to suit the individual clinical situation in each case. When a patient experiences disease onset before the age of 25 years and the disease affects only one generation autosomal recessive ataxias must be considered. If one of the patient's parents had a similar disease spinocerebellar ataxia (SCA) with a dominant autosomal mode of inheritance is probable. Patients with sporadic disease starting in adulthood may have an acquired ataxia, such as alcoholic cerebellar degeneration (ACD) or paraneoplastic cerebellar degeneration (PCD), or a sporadic degenerative ataxia, such as multiple system atrophy (MSA) or sporadic adult-onset ataxia (SAOA). Therapies based on the underlying molecular pathogenesis are available for a number of ataxia disorders.