Dystonic movements in a mutation of the Syrian golden hamster, named dtsz, have several features in common with clinically observed paroxysmal dystonic choreoathetosis. In this study the CNS of the mutant hamsters and age-matched nondystonic controls was examined for morphological alterations at the age of 30 days, i.e., when the severity of the dystonic syndrome is fully developed. Particular interest was directed to those brain regions (caudate nucleus, putamen, globus pallidus, ventrolateral thalamus) that are presumably involved in symptomatic dystonia of humans, as well as to regions (e.g., spinal cord, dorsal root ganglia, nucleus ruber) for which neuropathologically detectable lesions have been found previously in the dystonia musculorum mouse. The neuropathological investigation was carried out on routine paraffin histology on step sections of the whole brain and spinal cord. In addition, a silver impregnation method was used for detection of pre- and/or postsynaptic degeneration. Light microscopic examination, including morphometry, of the nervous tissue failed to reveal any morphological or morphometric differences between control and dystonic hamsters. The only abnormality that was found in several control and dystonic hamsters was hydrocephalus. Breeding studies using magnetic resonance imaging for detection of hydrocephalus showed that hydrocephalus was hereditary but not related to dystonia. Virus infections as a cause of hydrocephalus or dystonia could be excluded by serological analysis with determinations of various virus antibodies in hamster sera. The lack of neuropathological alterations related to dystonic movements in the present study in dtsz hamsters is comparable to most cases of human hereditary or idiopathic dystonia, which show dystonic movements in the absence of morphological alterations.