To investigate MR capabilities in assessing the extent of disease in chronic osteomyelitis of long bones, we examined 6 consecutive patients, 4 men and 2 women (age range: 27-67 years; mean: 42 years), with posttraumatic chronic osteomyelitis diagnosed at clinics, US, CT and radiography. The diagnosis had surgical or bioptical confirmation. MR studies were performed with an 0.5 T superconducting magnet, a surface coil and T1-weighted SE sequences-before and after Gd-DTPA administration-STIR and T2-weighted SE sequences, on the axial and coronal or sagittal planes. The signal intensity of the inflammation area was hypointense on short TR and TE images and hyperintense on long TR and TE images. After Gd-DTPA administration, granulation tissue surrounding the infection was enhanced in all cases and also the areas of vascularized inflammation within bone marrow were enhanced in two cases. MRI provided accurate and detailed information as to soft tissue and medullary canal involvement depicted sinus tracts in 5 cases and confirmed the presence of sequestrum in 5 cases, in agreement with previous CT findings. In our experience, MRI proved to be a reliable tool to assess the intramedullary and extracompartmental extent of osteomyelitis and also to plan surgery. MR specificity, which is often affected by post-traumatic or postoperative changes, improves markedly if some morphological features typical of the condition are also considered, such as sequestrum and sinus tracts.