Patients with traumatic brain injury (TBI) often present with seizures (functional and/or epileptic), but treatments for patients with TBI and seizures are limited. We examined treatment phase and 1-year post-enrollment outcomes following neurobehavioral therapy (NBT) for patients with TBI + functional seizures (FS) and TBI + epilepsy. In this multicenter, prospective, three-group, nonrandomized, controlled trial, with 1-year post-enrollment follow-up, three cohorts of adults were recruited: TBI + video-electroencephalography (EEG)-confirmed FS (n = 89), TBI + EEG-confirmed epilepsy (n = 29), and chart/history-confirmed TBI without seizures (n = 75). Exclusion criteria were recent psychotic or self-injurious behavior, current suicidal ideation, pending litigation or long-term disability, active substance use disorder, and inability to participate in study procedures. TBI + FS and TBI + epilepsy groups completed NBT for seizures, an evidence-based, 12-session, multimodal psychotherapy, whereas TBI without seizures participants received standard medical care. The primary outcome was change in seizure frequency; secondary outcomes were changes in mental health, TBI-related symptoms, disability, and quality of life. Reductions in average monthly seizures occurred during treatment in TBI + FS participants (p = .002) and were significant from baseline (mean = 16.75; 95% confidence interval [CI] = 11.44-24.53) to 12 months post-enrollment (mean = 7.28, 95% CI = 4.37-12.13, p = .002, d = .38). Monthly seizures decreased during treatment in TBI + epilepsy participants (p = .002); reductions were not statistically significant from baseline (mean = 2.38, 95% CI = 1.12-5.04) to 12-month postenrollment (mean = .98, 95% CI = .40-2.42, p = .07, d = .22). Regarding treatment-phase changes in secondary outcome measures, TBI + FS participants improved significantly on 10 of 19 variables (52.6%), TBI + epilepsy participants improved on five of 19 (26.3%), and TBI-onlycomparisons improved on only one of 19 (5.3%). NBT benefited patients with TBI + FS and TBI + epilepsy. Improvements were demonstrated at 1 year post-enrollment in those with TBI + FS. NBT may be a clinically useful treatment for patients with seizures.