Chronic dislocation of the radial head in children due to undiagnosed Monteggia lesion is uncommon. Although it can initially be asymptomatic, pain, restriction of movement and secondary arthritic changes may develop as the child grows. The treatment of chronic radial head dislocation remains controversial varying from benign neglect to surgical reduction. Only five chronic lateral Monteggia lesions have been described, with variable surgical results associated with redeslocation. A case of chronic post-traumatic lateral dislocation of the radial head in a child treated with ulna osteotomy rigidly fixed and reattachment of the annular ligament is presented. At 2 years follow-up the clinical result was very satisfying and concentric reduction was maintained. The authors conclude this may be an effective procedure for chronic post-traumatic lateral dislocation of the radial head in children.