Monteggia described a fracture of the proximal third of the ulna with anterior dislocation of the radial head from both the proximal radioulnar and radiocapitellar joints. The key treatment principle in Monteggia fractures is stable anatomic alignment of the ulna. We present an uncommon case of a Monteggia fracture-dislocation with an unreducable anterior dislocation of the radial head and associated with a lesion of the lateral collateral ligament of the elbow. The patient in our report had a successful clinical outcome and functional range of motion after rigid fixation of the ulnar shaft fracture and exploration of the elbow joint, reduction of the radial head and repair of the lateral collateral ligament. This case is unusual because of the association of a complete tear of the external collateral ligament of the elbow.