Radiographic examinations of the paranasal sinuses and chests of 187 patients with C.F. from five months to 27 years of age were reviewed. One hundred eight-five patients consistently had opaque maxillary and ethmoidal sinuses. Forty-five patients had normal chest radiographs. These observations show that the paranasal sinuses are almost always affected in children with C.F. Although opaque paranasal sinuses do not indicate the diagnosis of C.F., clear paranasal sinuses exclude this disease with reasonable certainty.