Although often reported in the literature, 'isolated' traumatic radial head dislocation in children is a rare condition which has not been studied extensively. There is very often a delay in diagnosis and treatment. Lincoln and Mubarak described the 'ulnar bow sign' in 1994. They accurately described the plastic deformity of the ulna and explained how to make a correct diagnosis from the radiographs. Probably most 'isolated' radial head dislocations in children are associated with plastic deformation of the ulna as stated in 1984 by Dubuc et al. (2). The recognition of these "plastic" Monteggia fractures is mandatory, as action on the ulna plays a central role in the treatment. On the other hand, the 'ulnar bow sign' may be used to detect subtle changes in the position of the radial head. We present 4 cases of chronic radial head dislocation associated with plastic deformation of the ulna. Open reduction of the radial head and reconstruction of the annular ligament was performed. An osteotomy of the ulna was deemed necessary in 3 cases.