Infantile onset spinocerebellar ataxia (IOSCA, MIM 271245) is a recessively inherited, progressive neurological disease, which we have described in 19 Finnish patients. The clinical symptoms of IOSCA include ataxia, athetosis, hypotonia, hearing deficit, ophthalmoplegia, sensory neuropathy, female hypogonadism, and epilepsy as a late manifestation. We have mapped the IOSCA locus to 10q24. In our two autopsy cases of IOSCA, the neuropathological findings were almost uniform. The cerebral hemispheres were quite well preserved, but the brain stem and the cerebellum were moderately atrophic. The most severe atrophic changes were seen in the spinal cord: in the dorsal roots, the posterior columns and the posterior spinocerebellar tracts. There was a severe neuronal loss in the dorsal nucleus (Clarke's column) of both cases and slight atrophy of the intermediolateral column in one case. The cerebellar peduncles, the inferior olives, the accessory cuneate nuclei and especially the dentate nuclei were atrophic and gliotic. The eighth cranial nerve and nucleus were atrophic. The ventral pontine nuclei and transverse fibers were slightly affected. Tegmental nuclei and tracts, especially sensory structures, were more severely affected. In mesencephalon, there was atrophy of the oculomotor nuclear complex and periaqueductal gray matter. The cerebellar cortex showed patchy atrophy. Degenerative changes were seen in dorsal root ganglia, and there was a severe axonal loss in the sural nerve. The neuropathological picture of IOSCA thus seems close to that reported in Friedreich's ataxia, another recessively inherited usually childhood-onset ataxia.