It is well established that women exhibit several anatomic and physiologic characteristics that distinguish their responses to exercise from those of men. These factors have been shown to influence the training response and contribute to lower maximal aerobic power in women. Additionally, the reproductive hormones, estrogen and progesterone, can influence ventilation, substrate metabolism, thermoregulation, and pulmonary function during exercise. Pulmonary structural and morphologic differences between genders include smaller vital capacity and maximal expiratory flow rates, reduced airway diameter, and a smaller diffusion surface than age- and height-matched men. These differences may have an effect on the integrated ventilatory response, respiratory muscle work, and in pulmonary gas exchange during exercise. Specifically, recent evidence suggests that during heavy exercise, women demonstrate greater expiratory flow limitation, an increased work of breathing, and perhaps greater exercise induced arterial hypoxemia compared to men. The consequence of these pulmonary effects has the potential to adversely affect aerobic capacity and exercise tolerance in women.