The infratemporal fossa is bordered superiorly by the infratemporal surface of the greater wing of the sphenoid bone and part of the temporal bone; medially by the lateral plate of the pterygoid process of the sphenoid bone; and anteriorly by the posterior surface of the maxilla. As it is completely surrounded by bone, it is frequently difficult to determine whether an abscess is present by direct visual observation or palpation alone. We report an extremely rare case of an infratemporal fossa abscess arising from chronic maxillary osteomyelitis developing after extraction of a maxillary molar. Despite drainage during initial oral anti-inflammatory treatment, pus continued to drain from the wound over a long period of time. This drainage ended when the eroded bone of the maxillary tuberosity on the affected side was curetted in a secondary procedure. The harvested bone tissue exhibited histological findings of chronic osteomyelitis. This suggests that the route of infection involved acute transformation of maxillary osteomyelitis by odontogenic infection advancing posteriorly and superiorly.