We examined whether striatal dopamine moderates the impact of externalizing proneness (disinhibition) on reward-based decision making. Participants completed disinhibition and substance abuse subscales of the brief form Externalizing Spectrum Inventory and then performed a delay discounting task to assess preference for immediate rewards along with a dynamic decision making task that assessed long-term reward learning (i.e., inclination to choose larger delayed versus smaller immediate rewards). Striatal tonic dopamine levels were operationalized using spontaneous eyeblink rate. Regression analyses revealed that high disinhibition predicted greater delay discounting among participants with lower levels of striatal dopamine only, whereas substance abuse was associated with poorer long-term learning among individuals with lower levels of striatal dopamine, but better long-term learning in those with higher levels of striatal dopamine. These results suggest that disinhibition is more strongly associated with the wanting component of reward-based decision making, whereas substance abuse behavior is associated more with learning of long-term action-reward contingencies.