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OBJECTIVE We aimed to prospectively quantify changes in white matter morphology after neurobehavioral therapy (NBT) for functional seizures (FS) using neurite orientation dispersion and density imaging (NODDI). We hypothesized that patients with FS would exhibit white matter plasticity in the uncinate fasciculus, fornix/stria terminalis, cingulum, and corticospinal tract following NBT that would correlate with improvements in affective symptoms, post-concussive symptoms, and quality of life (QOL). METHODS Forty-two patients with traumatic brain injury (TBI) and FS (TBI + FS) underwent NBT and provided pre-/post-intervention neuroimaging and behavioral data; 47 controls with TBI without FS (TBI-only) completed the same measures but did not receive NBT. Changes in neurite density (NDI), orientation dispersion (ODI), and extracellular free water (FW) were compared between groups. RESULTS Significant ODI increases in the left uncinate fasciculus in TBI + FS (mean difference = 0.017, p = 0.039) correlated with improvements in posttraumatic symptoms (r = -0.395, p = 0.013), QOL (r = 0.474, r = 0.002), emotional wellbeing (r = 0.524, p < 0.001), and energy (r = 0.474, p = 0.002). In TBI-only, ODI decreased (mean difference = -0.008, p = 0.047) and FW increased (mean difference = 0.011, p = 0.003) in the right cingulum. FW increases correlated with increased psychological problems (r = 0.383, p = 0.013). In TBI + FS, NBT resulted in FS decreases of 3.5 seizures per week. None of the imaging changes correlated with FS frequency. INTERPRETATION We identified white matter changes after NBT in patients with FS that were associated with improved psychosocial functioning. NODDI could be incorporated into future mechanistic assessments of interventions in patients with FS. This article is protected by copyright. All rights reserved.