The Iowa Gambling Task (IGT) is widely used to assess decision making under conditions of uncertainty in clinical as well as in nonclinical populations. However, there is still debate as to whether normal performance at this task relies on implicit, emotion-based processes that are independent of working memory. To clarify the role of working memory on normal performance on the IGT, participants performed the task under low or high working memory load. We used a modified version of the original task, in which the position of the four decks was randomized between trials. Results showed that only participants performing under low memory load significantly chose more advantageously halfway through the task. In addition, when comparing the number of cards chosen from the two decks with frequent losses, one advantageous and one disadvantageous, only participants performing under low memory load chose more cards from the advantageous deck. The present findings indicate that the processes underlying optimal advantageous performance on the IGT rely on working memory functions.