Objective: The impact of disrupted sleep on the effectiveness of prolonged exposure (PE) therapy for posttraumatic stress disorder (PTSD) is not well understood. Researchers have suggested that comorbid sleep disorders contribute to nonresponse by impairing therapeutic mechanisms such as emotional processing of trauma memories and extinction in cued fear conditioning. Several studies indicate daytime sleepiness, insomnia, and nightmares are correlated with PTSD symptom severity. However, a recent randomized controlled trial found that these sleep disorder symptoms did not affect PTSD symptom change over the course of massed PE (i.e., daily sessions across 2 weeks). Method: The current study used an ecologically valid clinical sample to examine whether daytime sleepiness, insomnia, and nightmares interfere with the slope of symptom change in massed PE. Results: Results indicate that all 3 sleep disorder symptoms correlate with PTSD symptom severity on the first day of treatment but were not associated with symptom change. Conclusions: These findings are consistent with the expectation that the daily structure of massed PE may enhance treatment engagement in patients who are typically drowsy or not well-rested, thus facilitating fear extinction. (PsycInfo Database Record (c) 2022 APA, all rights reserved)