In the clinical setting, Huntington's disease is associated with problems in judgment and decision making, however, the extent of these problems and their association with clinical characteristics have not been assessed. Recently, a laboratory-based simulated gambling task has been used to quantify similar decision-making deficits in ventromedial frontal lobe damaged participants. We hypothesized that participants with Huntington's disease (HD) would show deficits on this gambling task. For this study, 14 HD participants were asked to make 100 selections from four decks of cards with varied payoffs in order to maximize winnings of play money. They were compared to 22 participants with Parkinson's disease (PD) and 33 healthy controls. After an initial period in which participants had to learn contingencies of the decks, the HD group made fewer advantageous selections than the PD and control groups. In HD, the number of advantageous selections in the gambling task was correlated with measures of memory and conceptualization but not disinhibition. Thus, people with HD may have had difficulties learning or remembering win/loss contingencies of the decks, or they may have failed to consistently take these into account in their card selections. These findings are consistent with current models of frontal-subcortical brain circuits and behavior. (JINS, 2001, 7, 92–101.)