Multi-modal discourse comprehension requires speakers to combine information from speech and gestures. To date, little research has addressed the cognitive resources that underlie these processes. Here we used a dual task paradigm to test the relative importance of verbal and visuo-spatial working memory in speech-gesture comprehension. Healthy, collegeaged participants encoded either a series of digits (verbal load) or a series of dot locations in a grid (visuo-spatial load), and rehearsed them (secondary memory task) as they performed a (primary) discourse comprehension task. The latter involved watching a video of a man describing household objects, viewing a picture probe, and judging whether or not the picture was related to the video. Following the discourse comprehension task, participants recalled either the verbally or visuo-spatially encoded information. Regardless of the secondary task, performance on the discourse comprehension task was better when the speaker’s gestures were congruent with his speech than when they were incongruent. However, the congruency advantage was smaller when the concurrent memory task involved a visuo-spatial load than when it involved a verbal load. Results suggest that taxing the visuo-spatial working memory system reduced participants’ ability to benefit from the information in congruent iconic gestures.