Cannabis use is common among individuals with posttraumatic stress disorder (PTSD) symptoms, but its impact on psychiatric symptoms and functioning in this population is unclear. To clarify the clinical and functional correlates of cannabis use in individuals with PTSD symptoms, we analyzed data from the 2019–2020 National Health and Resilience in Veterans Study, a nationally representative survey of U.S. military veterans. Participants with current subthreshold or full PTSD (N = 608) reported on their past‐6‐month cannabis use and current psychiatric symptoms, functioning, treatment utilization, and PTSD symptom management strategies. Veterans with subthreshold/full PTSD who used cannabis more than weekly were more likely to screen positive for co‐occurring depression, anxiety, and suicidal ideation than those who did not use cannabis, ORs = 3.4–3.8, or used cannabis less than weekly, ORs = 2.7–3.7. Veterans who used cannabis more than weekly also scored lower in cognitive functioning than veterans with no use, d = 0.25, or infrequent use, d = 0.71, and were substantially more likely to endorse avoidance coping strategies, ORs = 8.2–12.2, including substance use, OR = 4.4, and behavioral disengagement, ORs = 2.7–9.1, to manage PTSD symptoms. Despite more psychiatric and functional problems, veterans with frequent cannabis use were not more likely to engage in mental health treatment, ORs = 0.87–0.99. The results suggest enhanced cannabis use screening, interventions targeting risky use, and strategies promoting treatment engagement may help ameliorate more severe clinical presentations associated with frequent cannabis use among veterans with subthreshold/full PTSD.