Hereditary ataxias, hereditary spastic paraplegia and Charcot-Marie-Tooth syndrome (HA) are chronic progressive neurological diseases. Epidemiologic studies of these disorders are few. In a geographically well-defined Danish population, we present incidence rates, cumulated incidence rates and prevalence for patients with HA based on modern continuous-time survival analysis techniques. From these, prevalence has been estimated to be 6.06 per 10(5) in the 10 to 50-year-old population. Combined risk of HA was found to be 0.16% for women and 0.20% for men up to their 51st birthday.