Background: Cognitive function of Machado-Joseph disease (MJD) patients has not been clarified.

Objectives: To determine the characteristics of cognitive dysfunction in MJD patients and to assess the relationship of dysfunction to age at onset, age at examination, disease duration, education, ataxia, depression, anxiety, and CAG repeat length.

Design: Case-control study.

Setting: Research-oriented hospitals.

Participants: Sixteen genetically confirmed MJD patients able to complete neuropsychological tests and 20 control subjects matched to patients by age and education.

Main outcome measures: Neuropsychological tests, including general cognition, verbal and visual memory, working memory, visuospatial and constructional ability, language, executive function, depression, and anxiety.

Results: Machado-Joseph disease patients scored significantly lower than controls in verbal and visual memory, in visuospatial and constructional tasks, and in phonemic and semantic fluency tasks. None of these impairments correlated with CAG repeat length, age at onset, age at examination, disease duration, or education. Verbal fluency (words named in a category) correlated with the International Cooperative Ataxia Rating Scale score.

Conclusion: Machado-Joseph disease patients have verbal and visual memory deficits, visuospatial and constructional dysfunction, and verbal fluency deficits, all unrelated to CAG repeat length.