Objective: This research studies the application of X-ray Cone beam computer tomography in diagnosis of mandibular third molar teeth. Subject and method: 46 patients consisting of 32 males and 14 females with mandibular teeth growing in deviation. All patients were x-rayed with film tomography Cone beam computer. Based on the result of the X-ray, the position and the size of the mandibular third molar teeth and mandibular second molar teeth are evaluated and the result of it will be used to determine tooth extraction. Result: The angle between the axis of the tooth and the mandibular third molar and second molar 45 degrees accounted for 11 percent. 45-90 degree angle accounted for 58 percent which is the highest rate. There was 48 percent of mandibular third molar teeth growing in proper order and 18 percent of its growing between supply teeth. The diameter sized 8-9 mm made up 52 percent. There were 11 teeth with one root, 20 teeth with 2-4 roots, 14 teeth with 2 separated roots, and 14 teeth with more than 2 separated roots. Conclusion: CT Cone-beam methods tomography diagnosed the exact location of mandibular third molar teeth which makes teeth extractions much safer.