Pneumosinus dilatans is a rare disorder of the frontal sinus most commonly found in 20- to 40-year-old males. The deformity is caused by an abnormal enlargement of the frontal sinus by hyperpneumatization. A valve mechanism raising the pressure inside the sinus is regarded to be responsible for this condition. The diagnostic and surgical approach is presented in a 25-year-old male. A preoperative computed tomography (CT) scan in three planes illustrates the anatomical conditions and possible etiologic mechanisms. The surgical procedure is supposed to correct the esthetic deformity and the cause of the disorder. A bicoronal incision allows the best exposition of the frontal sinus. The osteoplastic correction is stabilized by titanium micro-osteosynthesis plates, which do not have to be removed. Functional endoscopic sinus surgery should be performed concomitantly in order to remove the cause of pneumosinus dilatans.