OBJECTIVE: Sleep disturbances, including nightmares and insomnia, are frequently reported symptoms of posttraumatic stress disorder (PTSD). Insomnia is one of the most common symptoms to persist after evidence-based PTSD treatment. The purpose of this study was to examine the prevalence of sleep disturbances in a sample of active duty military personnel before and after receiving therapy for PTSD in a clinical trial and to explore the associations of insomnia and nightmares with PTSD diagnosis after treatment. METHOD: Sleep parameters were evaluated with the PTSD Checklist in 108 active duty U.S. Army soldiers who had completed at least one deployment in support of the wars in Iraq and Afghanistan and who participated in a randomized clinical trial comparing Group Cognitive Processing Therapy-Cognitive Only Version with Group Present-Centered Therapy. RESULTS: Insomnia was the most frequently reported symptom before and after treatment, with 92% reporting insomnia at baseline and 74%-80% reporting insomnia at follow-up. Nightmares were reported by 69% at baseline and by 49%-55% at follow-up. Among participants who no longer met criteria for PTSD following treatment, 57% continued to report insomnia, but only 13% continued to report nightmares. At baseline, 54% were taking sleep medications, but sleep medication use did not affect the overall results. CONCLUSIONS: Insomnia was found to be one of the most prevalent and persistent problems among service members receiving PTSD treatment. Nightmares were relatively more positively responsive to treatment. For some service members with PTSD, the addition of specific treatments targeting insomnia and/or nightmares may be indicated. (PsycINFO Database Record