Post traumatic stress disorder (PTSD) is associated with increased healthcare utilization, decreased functional status, and overall poor health. Sleep disturbances in PTSD are common, including nightmares, dream enactment, and poor sleep quality. Obstructive sleep apnea (OSA) is also highly prevalent in the veteran population and may exacerbate PTSD symptoms by triggering arousals from sleep that promote recollection of dreams, enactment of dreams, and disrupt sleep continuity. Improvements in sleep quality and PTSD symptoms have been reported when OSA is treated with continuous positive airway pressure (CPAP) therapy. However, formal assessment using validated questionnaires and documentation of CPAP compliance to correlate with these tools has not yet been performed. This study will recruit veterans with PTSD who have been newly diagnosed with OSA and who are willing to try CPAP therapy. Baseline assessments of PTSD symptoms, daytime sleepiness, sleep-related quality of life, sleep quality, general health perception, and mood will be performed before initiation of treatment and after 3 and 6 months of therapy.