OBJECTIVE This study compared mandibular and condylar mobility after open or closed treatment for fractures of the mandibular condylar process. METHODS One hundred thirty-six patients (111 male, 25 female), 74 treated by closed and 62 by open methods, were included in this study. They underwent testing of mandibular and condyle mobility at 6 weeks, 6 months, and 1, 2, and 3 years postsurgery. A jaw-tracking device was used to assess mandibular motion. Radiographs that were traced and digitized were used to assess condylar displacement and condylar mobility. Standard statistical methods were used to assess differences between groups. RESULTS Patients treated by open reduction had significantly greater initial displacement of their condylar processes than did the group treated closed. Immediately after treatment and uprighting of the condyles in the open treatment group, patients treated closed had significantly more displacement. At 6 weeks, patients treated closed had some measures of mandibular mobility that were significantly greater than those in patients treated by open reduction. However, after the 6-week period there were minimal differences in mandibular mobility between groups. At 6 weeks, patients treated by open reduction had significantly greater vertical mobility of the condyle than patients treated closed despite less mouth opening. After the 6-week period, patients treated by open reduction continued to have greater condylar mobility on the fractured side than did patients treated by closed methods. No measures of postsurgical displacement correlated with mobility measures in patients treated by open reduction. However, several measures of mandibular displacement correlated with measures of mobility in patients treated closed, indicating that the more displaced the condylar process, the more limited the mobility of the mandible. CONCLUSIONS Based on this study, patients treated for fractures of the mandibular condylar process by open reduction had somewhat greater condylar mobility than patients treated closed, even though the former group had more severely displaced fractures before surgery. Therefore, open reduction may produce functional benefits to patients with severely displaced condylar process fractures.