The aim of the study was to evaluate the influence of a mandibular protruding device (MPD) after 2 years of nocturnal use on the upper airway and its surrounding structures. Lateral cephalograms in the upright position were taken of patients with obstructive sleep apnea (OSA) and of patients with snoring problems at the beginning of treatment and at the 2-year follow-up. Two computer programs were used to analyze the cephalograms. A total of 65 patients, 44 with OSA and 21 snorers, were analyzed. The linear distances in the pharynx had increased significantly at the 2-year follow-up; the calculated pharyngeal area had increased on average by 9% (mean, +58.3 mm(2)). The velum area had decreased (mean, -31.5 mm(2)), which accounts for about half the increase in the relative area of the pharynx. The average linear distances between the hyoid bone and the 2 reference lines, ie, nasal line (NL) and mandibular line (ML), had increased significantly. Mandibular protrusion (SNB) was slightly reduced, on average -0.4 degrees (P <.01), and the lower incisors were proclined (ILi/ML), on average +1.5 degrees (P <.05). In conclusion, nocturnal use of an MPD for 2 years increased the airway passage because of an increase in the relative area of the pharynx by a mean of 9% in OSA patients and snorers. A mandibular posterior rotation and a proclination of the lower incisors were observed but considered modest.