Mandibular prognathism is a common developmental jaw deformity with functional disabilities and facial disfigurement, characterised by a prominent mandible. Very satisfying cosmetic and functional results can be achieved by surgery and the literature is replete with surgical techniques for correcting this deformity. This paper discusses the surgical treatment of mandibular prognathism and reviews a series of 25 consecutive patients treated by an extra-oral technique known as Subsigmoid Oblique Osteotomy (Vertical Subcondylar Osteotomy) during a seven-year period, (1969-76).