Background: Caffeine use is highly prevalent among active duty military personnel and can be beneficial to performance in the short term. However, regular caffeine use has been found to contribute to sleep disturbances, which are elevated among the significant number of military personnel with posttraumatic stress disorder (PTSD). The current study is the first to examine caffeine use and its relationship with sleep disturbances in military personnel seeking treatment for PTSD. Participants: Active duty military personnel (N = 366) who had returned from deployments to Afghanistan or Iraq and were seeking treatment for PTSD. Methods: Pearson correlations were used to examine the relationships between caffeine use, sleep disturbances, and PTSD symptom clusters. Results: The majority of the sample (89%) reported some caffeine use, with coffee being the largest contributor to total caffeine intake. Contrary to hypotheses, higher caffeine use was associated with lower insomnia symptom severity; follow-up analysis indicated that this was due to elevated insomnia symptom severity in those reporting no caffeine use. Caffeine use was not associated with any other measures of sleep disturbance or with PTSD symptoms. Conclusions: Caffeine use was not associated with greater reported sleep disturbances in this sample, possibly because those with elevated insomnia symptom severity abstained from any caffeine, or because insomnia symptoms were elevated in this sample.