Since there exists no standard interface for simulations, simulation systems must be designed for operation by individuals with very limited experience with the specific training system. Therefore, designers have begun to integrate menu systems into the control schemes of simulations. While menus excel in providing an inexperienced user with easy access to system functionality, they must be properly designed in order to achieve maximum benefit to the user. Many menu-driven tasks must be performed simultaneously with other vital tasks; therefore it is important to develop a better understanding of the effects of divided attention on performance in a menu-driven application. Very little research has been directed toward understanding how menu design features interact with a decrease in available attentional resources due to division of attention across two or more simultaneous tasks. The current study examined the effects of adding an auditory discrimination secondary task to the primary task of interacting with a menu-driven interface. Differences were observed in the patterns of performance and subjective workload under task load among these interface designs. Contrary to previous research, the color coded menu design was not found to improve robustness to secondary task load, and yielded significantly higher subjective workload in the higher task load condition. Performance on the low density menu design was found to be particularly vulnerable to secondary task load, and this finding was reflected in higher subjective ratings of workload in the high task load condition. The grouped menu design, however, yielded no significant degradation in performance in the high task load condition, although significantly higher workload was observed under higher task load. These findings will be discussed in the context of attentional resource allocation, and design recommendations will be made with regard to menu systems intended for use in simulations.