The effect of orthodontic-surgical treatment on submental-cervical region was evaluated in a very limited number of studies. The aim of this study was to evaluate submental-cervical soft tissue contour changes following mandibular advancement and set-back procedures via bilateral sagittal split ramus osteotomy. Sixty-seven patients were included in this study. Group 1 consisted of 27 skeletal Class II patients who underwent mandibular advancement surgery, whereas Group 2 consisted of 40 skeletal Class III patients who underwent mandibular set-back surgery. Various linear and angular measurements were performed on pre-operative and sixth month post-operative cephalometric radiographs. A new method was used to evaluate the amount of sagging at submental region. The submental length did not change in Group 1; however, it decreased significantly in Group 2 (P < 0·05). The angle between submental plane and facial plane decreased to 95·9° from 98·8° in Group 1(P < 0·05), whereas it increased to 93·1° from 88·2° in Group2 (P < 0·05). The change of submental soft tissue sag was almost stable in Group 1, while 0·34 mm increase of sag was observed in Group 2. This increase was not statistically significant (P > 0·05). Mandibular set-back and advancement procedures do not remarkably change the submental sag following approximately 6 mm jaw movement. Although mandibular advancement did not significantly effect submental length, soft tissue followed mandibular set-back with a ratio of 1:1 at C-point to projection of soft tissue pogonion and 1:0·7 at C-point to soft tissue menton distances.