A 22-year-old male patient had developed a submasseteric abscess secondary to a mandibular osteomyelitis at the age of 7 years old. The initial presentation at that time seems to be acute suppurative parotitis. The computed tomographic scans taken before surgery demonstrated diffuse deformity, sclerotic change and osteolytic lesion in the mandible. There was no marrow space on both sides of mandibular ramus and thin-walled cortical bone was seen. So, from the results of the computed tomography, the surgery was performed intraoral vertical ramus osteotomy (IVRO) instead of performing the more commonly used bilateral sagittal split ramus osteotomy (BSSRO). In this report, we present a case of surgical correction of mandibular prognathism with fibrous-osseous lesion of mandible with using IVRO.