Medullary bone infarctions, which are believed to arise due to arterial obstructions in the bone, are usually asymptomatic and are noted incidentally in roentgenograms or bone scans performed for other reasons. We present two cases of acute bone infarctions that were found accidentally by magnetic resonance imaging (MRI). In both cases, conventional radiographs could not demonstrate any findings and the cases were clinically asymptomatic. The current two cases suggest that MRI shows various findings in bone infarctions.