Past work examining the effects of interruption complexity on primary task performance has yielded quite mixed results. Some research suggests that more complex interruptions lead to greater disruption of the primary task, while other studies have shown that interruption complexity does not directly influence the amount of primary task disruption. It is our hypothesis that interruption complexity, defined by the number of mental operators required to complete a task as opposed to an intuitive sense of difficulty, does affect primary task performance, such that interruptions requiring more mental operators (more complex) lead to greater disruption than do less complex interruptions. Participants performed a single primary task in conjunction with either a simple or complex interruption. The complex interruption required more mental operators to complete than the simple interruption. Our results showed that it took longer to resume the primary task following a complex interruption than it did following a simple interruption. These results suggest that more complex interruptions, as quantified by the number of mental operations required, do indeed lead to greater primary task disruption.