Objectives: To assess the role self-reported treatment for a psychiatric diagnosis may play in long-term functional outcomes after operatively managed tibial plateau fractures. Design: Prospective cohort study. Setting: Academic medical center. Patients: Over an 11-year period, patients were screened and identified on presentation to the emergency department or in the clinical office for inclusion in an IRB-approved registry. A total of 245 patients were included in the study. Twenty-one patients reported treatment for a psychiatric diagnosis. Intervention: Surgical repair of tibial plateau fractures. Main Outcome Measure: Patients were divided into 2 cohorts; 1 cohort being those who self-reported receiving treatment of a psychiatric diagnosis (PI); the other group being those who did not self-report receiving treatment of a psychiatric diagnosis (NPI). Three-month, 6-month, and long-term outcomes (mean = 18 months) were evaluated using the Short Musculoskeletal Function Assessment (SMFA), pain scores, and postoperative complications (infection, VTE, nonunion, and necessity for secondary operations). Results: Pain scores were higher in patients who self-reported receiving treatment for a psychiatric diagnosis (P = 0.012). Longterm functional outcomes as measured by the SFMA were demonstrated to be worse in patients who self-reported treatment for a psychiatric diagnosis (P = 0.034). No differences existed between groups in regards to postoperative complications. Multiple linear regression analysis revealed that being treated for diagnosis of a mental health illness was an independent predictor of worse functional outcomes at long-term follow-up [B = 8.874, 95% confidence interval (CI) = 0.354-17.394, P = 0.041]. Conclusions: Mental health plays a crucial role in long-term outcomes after operative fixation of tibial plateau fractures. Patients who have been diagnosed with a mental health illness have significantly worse outcomes at long-term follow-up.