Objective: Acceptance and commitment therapy (ACT) is a widely utilized psychotherapeutic approach, but randomized, controlled studies are lacking in veterans. This study evaluated the efficacy of ACT for emotional distress among veterans of the conflicts in Iraq and Afghanistan. Method: One hundred sixty veterans (80% male, Mage = 34 years) with anxiety or depressive disorder according to the Diagnostic and Statistical Manual of Mental Disorders (4th ed.) were randomized to ACT or present-centered therapy (PCT) and assessed before, during, and after treatment and during 3- to 12-month follow-up. The primary outcome was general distress as measured by the Brief Symptom Inventory–18 Global Severity Index. Additional outcomes included symptomatology, disability, quality of life, acceptability, and satisfaction. Results: There was improvement following treatment in the whole sample across a variety of measures, including general distress (d = 0.74, 95% confidence interval [CI: 0.52, 0.96]) and functioning (d = 0.71, 95% CI [0.50, 0.93]) and moderate to high levels of satisfaction with treatment. Response to the 2 interventions did not differ on the primary outcome or most secondary outcomes, although ACT led to greater improvement in insomnia than did PCT (ds = 0.63 and 0.08, respectively). Treatment dropout did not differ by condition but was high (41.9%). Conclusions: ACT’s efficacy in this group was modest and generally did not differ from that for PCT. Additional work is needed to understand the reasons that ACT did not perform as well as predicted in this veteran sample.