The current study sought to examine whether lifetime PTSD symptom severity is associated with a bias toward sampling extreme negative events from memory when making decisions involving uncertainty. To this end, 40 trauma-exposed warzone veterans performed a decision task in which information about outcomes was learned through experience and making choices required sampling memories of past experiences. On each trial, participants made choices between certain and uncertain gains and between certain and uncertain losses. Uncertain outcomes were equally likely to yield a relatively positive or relatively negative outcome. After accounting for overall willingness to take risks, lifetime PTSD symptom severity was associated with less frequent choice of the uncertain option for gains and for losses, a pattern consistent with a memory sampling bias for all negative experiences rather than only extreme negative experiences. The overweighting of negative experiences as a function of lifetime PTSD symptom severity, however, was not observed in a subsequent explicit memory task in which participants estimated the frequency with which different outcomes had occurred during the decision task. These findings suggest that the memory mechanism responsible for the PTSD-associated memory bias in decision making is distinct from that mediating explicit memory performance.