Recent research has documented high rates of comorbidity between cannabis use disorders and posttraumatic stress disorder (PTSD) in veterans. However, despite possible links between PTSD and cannabis use, relatively little is known about cannabis use in veterans who present for PTSD treatment, particularly among samples not diagnosed with a substance use disorder. This study examined the prevalence of cannabis use and the psychological and functional correlates of cannabis use among a large sample of veterans seeking treatment at a Veterans Affairs (VA) PTSD specialty clinic. Male veterans (N = 719) who presented at a VA specialty outpatient PTSD clinic completed measures of demographic variables, combat exposure, alcohol, cannabis and other drug use, and PTSD and depressive symptoms. The associations among demographic, psychological, and functional variables were estimated using logistic regressions. Overall, 14.6% of participants reported using cannabis in the past 6 months. After controlling for age, race, service era, and combat exposure, past 6-month cannabis use was associated with unmarried status, use of tobacco products, other drug use, hazardous alcohol use, PTSD severity, depressive symptom severity, and suicidality. The present findings show that cannabis use is quite prevalent among veterans seeking PTSD specialty treatment and is associated with poorer mental health and use of other substances. It may be possible to identify and treat individuals who use cannabis in specialty clinics (e.g., PTSD clinics) where they are likely to present for treatment of associated mental health issues.