A former healthy 22 year old man developed chronic hematogenous osteomyelitis of his right fibula. Ongoing disease unresponsive to antibiotic treatment led to operative debridement, despite the CT scan that showed no sequester formation. During the operation however, a large sequester of the fibula incorporated by an involucrum was found. We believe it is important to be cautious for this uncommon complication of osteomyelitis, even when radiologic imaging is suggesting otherwise. In case of progressive disease in a conservatively treated patient, surgical debridement is advised.