Obstructive sleep apnea, (OSA) is a sleep disorder traditionally associated with high blood pressure, cardiovascular disease, and/or obesity in which an obstruction of the upper respiratory airflow occurs in patients. This airflow disruption is repeated resulting in a cyclical breathing pattern that leads to frequent arousals during sleep. Epidemiological analyses of OSA have found that the disorder occurs more frequently in men than women. Yet, the severity of OSA-associated comorbidities are worse in women than in men upon initial OSA-diagnosis. The primary reasons for sex differences in OSA are thought to be associated with variations seen in normal sleep between men and women, distinctions in the clinical manifestations of sleep disturbances, and in the prevalence of risk factors for sleep disorders. However, it has also been suggested that this sex difference is due to an under-diagnosis of OSA in women during the early stages of the disease, as initial presentation of female patients with OSA has often been interpreted as depression and/or insomnia. Due to the risk factors associated with OSA, heart disease as the leading cause of death in both men and women in the United States, and the commonality of sex differences in sleep disorders, we examined the literature to determine what may contribute to these sex differences in OSA. This brief review summarizes what may be the causes of sex differences in normal sleep, sex differences that are associated with OSA, and whether this sex difference may be primarily due to an under-diagnosis of OSA in women.