Assessment of acute mild traumatic brain injury (mTBI) symptoms after a combat blast could aid diagnosis and guide follow-up care. Our objective was to document acute mTBI symptoms following a combat blast and to examine associations between acute symptoms and mental health and service discharge outcomes. A retrospective cohort study was conducted with 1656 service personnel who experienced a combat blast-related mTBI in Iraq. Acute mTBI symptoms were ascertained from point-of-injury medical records. The associations between acute symptoms and posttraumatic stress disorder (PTSD), postconcussion syndrome (PCS), and type of service discharge were examined. Disability discharge occurred in 11% of patients, while 36% had a non-disability discharge and 52% had no recorded discharge. A PTSD and PCS diagnosis was made in 19% and 15% of the sample, respectively. The most common acute mTBI symptoms were headache (62.8%), loss of consciousness (LOC) (34.5%), and tinnitus (33.2%). LOC was predictive of PTSD (odds ratio [OR] 1.54; 95% confidence interval [CI] 1.18, 2.00) and PCS (OR 2.08; 95% CI 1.56, 2.77), while altered mental status (OR 1.53; 95% CI 1.07, 2.17) and previous blast history (OR 1.83; 95% CI 1.15, 2.90) also were predictive of PCS. While no acute mTBI symptoms were associated with discharge outcomes, injury severity was associated with disability discharge. LOC after blast-related mTBI was associated with PTSD and PCS, and injury severity was predictive of disability discharge. The assessment of cognitive status immediately after a blast could assist in diagnosing mTBI and indicate a need for follow-up care.