The purpose of this study was to examine executive functioning in patients with Huntington's disease using an arithmetic word-problem-solving task including eight solvable problems of increasing complexity and four aberrant problems. Ten patients with Huntington's disease and 12 normal control subjects matched by age and education were tested. Patients with Huntington's disease performed the solvable problems significantly worse than the normal control subjects, but there was no difference in performance between the two groups in inhibiting aberrant problems. These results suggest that early Huntington's disease patients exhibit a precocious impairment in their ability to plan the resolution of complex arithmetic word problems without deficit in their ability to eliminate aberrant problems. This dissociation of performance fits with what we have found in such patients using script-sequencing tasks (Allain et al., 2004) and with neuropsychological data obtained by Watkins et al. (2000). These results are consistent with what is known about the neuropathological progression of Huntington's disease in which neuronal loss progresses in a dorso-to-ventral direction and with what was shown in patients with circumscribed frontal lobe damage. In these patients, impairments in planning solvable word problems were more frequent when lesions were in the lateral prefrontal regions.