["Journal of Traumatic Stress, EarlyView. ", "\nAbstract\nThe co‐occurrence of mild traumatic brain injury (mTBI) and posttraumatic stress disorder (PTSD) is associated with greater impairment relative to the presence of either condition alone. This study evaluated the effectiveness of cognitively augmented behavioral activation (CABA) therapy, compared to treatment as usual (TAU), at reducing mTBI and PTSD symptoms in 71 military veterans randomized to treatment at two urban U.S. Department of Veterans Affairs medical centers. Primary outcomes were PTSD symptom severity, measured by structured clinical interview (Clinician‐Administered PTSD Scale for DSM‐5; CAPS‐5) and self‐report questionnaire (PTSD Checklist for DSM‐5; PCL‐5), and objective cognitive function (neuropsychological test battery). Intent‐to‐treat analyses using linear mixed‐effects regression models (LMM) indicated that CABA significantly outperformed TAU in reducing PTSD symptom severity, CAPS‐5: d = 0.11, p = .027, PCL‐5: d = 0.11, p = .030 (small effects), and improving performance on neuropsychological tests of verbal learning, d = 0.07 (small effect) and delayed recall, d = 0.26 (small‐to‐medium effect). Changes in PTSD symptoms were explored via within‐group LMM, which revealed significant within‐CABA reductions, CAPS‐5: d = 0.87, p < .001, PCL‐5: d = 0.40, p = .006 (medium‐to‐large effects), but no significant symptom change within the TAU group, CAPS‐5: d = 0.07, p = .195, PCL‐5: d = 0.00, p = .978 (small effects). There was no significant difference between groups on treatment satisfaction ratings. This randomized controlled trial provides preliminary evidence that CABA may be a promising intervention for comorbid mTBI and PTSD.\n"]