Fracture of proximal two-thirds of ulna and dislocation of the proximal radio-ulna joint in the same upper limb is called Monteggia fracture- dislocation. Four clinical variants of this fracture- dislocation have been described according to Bado__ampersandsignrsquo;s classification depending upon the fracture location and direction of dislocation of the radial head. Monteggia fracture-dislocation type 3 is a rare variety and its association with posterior interosseous nerve injury is not widely documented. We report the case of a 13 year old male who presented with one day old history of painful and swollen left elbow and weakness of his ipsilateral hand, following a self fall. On careful clinical examination and imaging (x-ray), he was diagnosed to have sustained Monteggia type 3 fracture-dislocation with posterior interosseous nerve (PIN) injury. After adequate pre-operative follow-up, the patient was treated by open reduction of the radial head, annular ligament reconstruction and open reduction, internal fixation of the fracture ulna with DCP and screws. The patient was followed up at regular intervals. His recent radiograph of the left forearm and elbow shows satisfactory union at the fracture site with complete recovery of the posterior interosseous nerve injury.