Mandibular periostitis ossificans was assessed in a 18-year-old black boy. This form of chronic osteomyelitis (Garré osteomyelitis) resulted from a periostitis on the 4.8 in association with an infected and ankylosed 4.7. Clinically a firm swelling of the right mandibular angle was noticeable. The diagnosis was confirmed by computed tomography and biopsy. After extraction of the causative teeth, in combination with an antibiotic treatment, a good evolution was obtained. The possible pathogenesis and the differential diagnosis are discussed.