Introduction: Monteggia fracture–dislocation (MFD), defined by proximal ulna fracture with radial head dislocation, is an uncommon injury with potential for persistent pain, stiffness, instability, and loss of forearm rotation when reduction and alignment are suboptimal. Evidence on durability of recovery beyond the early healing phase remains limited. This study evaluated long-term functional outcomes and complications after MFD managed at a tertiary trauma center. Materials and Methods: A retrospective observational study was conducted using electronic medical records and PACS imaging. Forty consecutive patients with radiologically confirmed MFD and ≥12 months follow-up were included. Injuries were classified by Bado type. Treatment details (operative vs non-operative, ulnar fixation method, need for radial head open reduction, adjunct annular ligament procedures) and complications were recorded. Radiographic union and range of motion were extracted from follow-up documentation. Functional outcome at final follow-up was graded using Anderson et al. criteria (excellent/satisfactory/unsatisfactory/failure) based on union and loss of elbow flexion–extension and forearm rotation. Associations between Bado type and dichotomized outcome were tested (χ²/Fisher’s exact), with p20° elbow flexion–extension loss and 20% had >50% forearm rotation loss. Complications occurred in 35%, most commonly stiffness requiring supervised physiotherapy >3 months (15%). Anderson outcomes were excellent in 45% and satisfactory in 35% (combined 80%); unsatisfactory and failure were 15% and 5%, respectively. Bado type was not significantly associated with outcome (p=0.257). Conclusion: Most adult MFDs achieved union and good functional results with operative fixation, especially plate stabilization of the ulna, and radial head reduction was commonly restored by correcting ulnar alignment. However, a substantial minority experienced clinically relevant motion loss and complications, highlighting the need for anatomic reconstruction, verification of radiocapitellar congruity, and structured rehabilitation.