<p>Medication-related osteonecrosis of the jaw (MRONJ) is primarily diagnosed based on clinical criteria; however, maxillary lesions with sinus disease may present with overlapping clinicopathologic features. We report a case of maxillary sinus aspergillosis with osteomyelitis clinically mimicking MRONJ in a 73-year-old woman receiving long-term oral bisphosphonate therapy for osteoporosis. The patient presented with delayed healing after tooth extraction, bone exposure, purulent discharge, and an oroantral communication, fulfilling the clinical criteria for stage 3 MRONJ. Computed tomography demonstrated a unilateral maxillary sinus lesion with adjacent sclerosis but without intralesional calcification. Partial maxillectomy was performed, and a fungal mass was identified intraoperatively. Histopathological examination revealed inflammatory osteomyelitis without definite necrotic bone, whereas the sinus contents demonstrated Aspergillus species on Grocott staining. No angioinvasion was identified. These findings supported maxillary sinus aspergillosis with associated osteomyelitis as the dominant pathology, although coexisting MRONJ could not be completely excluded because of the clinical criteria fulfilled, long-term bisphosphonate exposure, and partial sampling. This case highlights a diagnostic pitfall, emphasizing that MRONJ criteria are not disease-specific and that fungal sinus disease should be included in the differential diagnosis of maxillary lesions with sinus involvement.</p>