Here we investigate the effect of sound on the perception of visual realism and the time required to complete a simple navigation-based task within a serious gaming (virtual) environment under various sound and visual conditions. Results indicate that the perception of visual realism and task completion time can be affected by sound. Designers and developers of serious games (and virtual environments in general) should be aware of the effects of sound on a user's perception of the visual scene and on task completion time, and they should thus ensure that sound is carefully considered when creating such environments.