The purpose of this study was to investigate the biomechanical relationship between the condylar and anterior guidances in deep bite malocclusion and control groups. The subjects consisted of 18 deep bite patients and 14 normal occlusions. A four-bar mechanism was described on the lateral cephalogram films and a computer program, for which the lengths of the links measured on the films were the inputs, was developed. The computer program was used to calculate the angles of rotation of the mandible and the condyle during contact of the mandibular anterior teeth with the lingual surface of the maxillary anterior teeth as the mandible moves forward. Comparison of the mean values of the angles of rotation of the mandible and condyle in the two groups has shown that the change in the angle of rotation of the condyle is statistically significant (P < 0.05). The angles of rotation of condyle in deep bite group were found larger than the angles of normal group. Correlation between the angles of rotation of the condyle and mandible has shown that they were significantly related. The cause of temporomandibular disorders may be attributed to the large angle of rotation of the condyle in deep incisal overbite.