Congenital radioulnar synostosis is a rare condition, only 400 cases have been reported in the world literature. Often bilateral, it can be recognised from birth by a clinical examination if it is attentive (examination of the prono-supination of the two elbows). It is in fact often discovered later, especially in unilateral forms, in children of school age. The proximal congenital radioulnar synostosis often results in functional, cosmetic limitations of the upper limb, especially in the bilateral forms. Rotational osteotomy through the synostosis site is the usual procedure. The techniques and sites envisaged for this surgery are numerous, with multiple difficulties, risks and possible complications. We propose the observation of an eight-year-old boy with an asymptomatic form of proximal radioulnar synostosis. The surgical treatment consisted of a resection of the synostosis with rotational transverse osteotomy of the two bones of the forearm completed by a plaster in a neutral position. Clinical results, evaluated at an average of twelve months postoperatively, were found to be satisfactorily on aesthetic and functional levels. The aim of our work is to highlight our straightforward and reliable surgical procedure of the osteotomy of the synostosis maintained by spindles, allowing the functional improvement of the movements of the forearm of our child and thus a healthy life.