The hallmark of osteomyelitis was progressive bone destruction and sequestrum formation. In the underlying disease, like diabetes mellitus, osteomyelitis becomes severe and exacerbates the condition. It was essential for the oral and maxillofacial surgeon to comprehend its complex medical and surgical management to achieve complete disease eradication. The aim of this article was to report a rare case and comprehensive management of extensive sequestrating maxillary osteomyelitis with uncontrolled diabetes mellitus patients. A 58-year-old male patient with pain and swelling accompanied by discharge of pus in the sinistra maxilla region. The systemic disease was identified as uncontrolled diabetes mellitus, and had a history of unhealing wounds 1 year ago after upper left molar extraction. Computed tomography scan result showed extensive sequester formation and bony destruction in the right extending to the left maxilla. Microbial culture results were Klebsiella pneumoniae and Morganella morganii. Subsequently, extensive sequestrectomy and multiple extractions of the involved jaw and teeth were performed after diabetes mellitus was regulated. A suspension suture against oral and nasal mucosa was performed to avoid dead space formation. Comprehensive perioperative management in maxillary osteomyelitis in uncontrolled diabetes mellitus includes sequestrectomy, definitive antibiotic therapy based on culture results, and diabetes regulation to improve the successful management of this case.