In mandibulectomy patients who have not undergone surgical reconstruction, the remaining mandibular segment is unstable and often deviated. Its movements have low reproducibility during mastication, deglutition and speech. The purpose of this study was to clarify three-dimensionally the differences in mandibular movements for each of these oral functions in mandibulectomy patients with and without mandibular continuity. Four mandibulectomy subjects (Group I) without mandibular continuity and three subjects (Group II) with mandibular continuity were selected. Their mandibular movements were recorded using a jaw movement tracking device with six degrees of freedom. Each movement was assessed graphically at the virtual incisor point and the rotational angles of the mandible in the frontal, sagittal and horizontal plane were analyzed. The findings were as follows; 1. In Group I, the border movements at the virtual incisor point exhibited an irregular and asymmetric envelope deviated to the resected side in the frontal plane, whereas Group II exhibited a smooth and symmetric envelope. 2. In Group I, the rotational angles in the frontal plane during border movements and mastication, in all planes during speech, and in the frontal and horizontal plane during deglutition were significantly larger than in Group II. A comparison among border and all functional movements in mandibulectomy patients revealed characteristic movements in the rotation of the mandible in the frontal plane. It is suggested that the rotational angle of the mandible is a useful parameter for assessment of mandibular movements in mandibulectomy patients.