Diagnosis of ischemic bone lesions relies on medical imaging, as clinical presenting features, if any, lack specificity. MR imaging is the imaging modality of choice for their detection and classification. Systemic osteonecrosis can be accurately recognized on MR images as a peripheral rim of low and high signal intensity surrounding the necrotic lesion. In the setting of systemic osteonecrosis, necrotic marrow lesions are frequently multiple and asymptomatic. Many risk factors are associated with this condition, such as the use of corticosteroids and alcohol abuse. The spontaneous occurrence of a fracture is the most frequent complication and develops almost exclusively in epiphyseal ischemic lesions. Posttraumatic osteonecrosis is a relatively rare complication of fracture and joint dislocation. This lesion pattern involves a specific situation, such as the femoral head after subcapital fracture and hip dislocation, the humeral head after displaced proximal fracture, and the talus. The lesion pattern at MRI is similar to that of systemic osteonecrosis.