The purpose of this study was to investigate the usefulness of magnetic resonance imaging (MRI) in the diagnosis of, and when deciding on treatment policies for, vertebral fractures in patients with osteoporosis by comparing the diagnostic success rates for such fractures using MRI and plain radiographs. We also devised a new classification of vertebral fractures in osteoporotic patients based on MRI findings. The subjects were 34 patients with a total of 316 osteoporosis-related vertebral fractures treated in our department during the past 2 years. They consisted of 30 women and 4 men with an average age of 82 years (range 61-95 years). The site diagnostic rates of plain radiographs and MRI for the vertebral fractures were compared, and changes in signal intensity of the fractured vertebrae in MRI were examined. The areas of change in signal intensity in T1-weighted sagittal images were classified into six types: total, anterior, posterior, superior, inferior, central. The site diagnostic rate for vertebral fractures was 98% for MRI, which was better than the 87% obtained with plain radiographs. Changes in signal intensity in the vertebrae showed no intraspinal protrusion in the inferior and superior types, and neurological stability was achieved; but there was a high frequency of intraspinal protrusion in the total and posterior types.