Predictability of aversive events impacts the development and maintenance of anxiety, particularly panic disorder. Although animal studies typically have found a preference for signaled (predictable) over unsignaled (unpredictable) aversive events, results of research with human participants have been less clear. Using a panic-relevant paradigm, the authors examined predictability preference with humans as a function of anxiety sensitivity and gender during repeated administrations of 20% carbon-dioxide-enriched air. Participants preferred predictable administrations, with high-anxiety individuals showing greater preference than low-anxiety individuals and women showing greater preference than men. In addition to providing information to better understand human predictability preference for panic-related events, results also may aid in determining the applicability of predictability to the cognitive-behavioral treatment of panic disorder.