Our aim was to evaluate the accuracy of magnetic resonance imaging (MRI) and bone scintigraphy in the diagnosis of mandibular osteomyelitis. Twenty patients with mandibular osteomyelitis were prospectively investigated by conventional radiography, bone scintigrams and MRI. All diagnoses were verified either by surgery or by the clinical course. There was no significant difference between bone scintigraphy and MRI in the detection of osteomyelitis or the assessment of its extent. MRI was significantly better than scintigraphy at detecting the presence and assessing the extent of extraosseous inflammation. We always use MRI to diagnose osteomyelitis. For long-term follow-up of patients with mandibular osteomyelitis, we recommend MRI and bone scintigraphy.