The authors reports on the case of a young, 17-year-old girl, suffering from Noonan's syndrome, with a bilateral conductive hypoacusia. Surgical exploration of the tympanic cavity revealed on one side an attical fixing of the ossicular chain and on the other side a hyperlaxity of the incudostapedial joint. On the basis of this observation, they stress the neglect of a study of the hearing of such patients, whose verbal expression and intellectual level are also impaired. Finally, they study the type of deafness involved and its etiopathology, suggesting the hypothesis of an anomaly in the development of the first branchial arch.