PURPOSE: To differentiate multiple myeloma from metastasis involving the spine at MR imaging. MATERIALS AND METHODS: Twenty-five patients with multiple myeloma and 37 with vertebral metastasis were included in this study. MR images were retrospectively analyzed with regard to infiltration and enhancement patterns, signal intensity, the involvement of three consecutive vertebrae, the number of lesions within one vertebra, and paraspinal and epidural masses. Using a 1.5-T imager, we obtained sagittal and axial, unen-hanced and enhanced T1-weighted images, and fast spin-echo images. For statistical analysis, Fisher's exact test was used. RESULTS: All cases of multiple myeloma and metastasis showed low signal intensity on T1-weighted images, and there were no significant differences in signal intensities or enhancement patterns. Infiltration and enhancement patterns were classified as focal (52% in multiple myeloma vs 68% in metastasis, p> 0.05), diffuse (32% vs 32%, p > 0.05) or salt and pepper (16% vs 0%, p < 0.05) pattern. Differentiation between multiple myeloma and metastasis was based on two criteria: the involvement of three consecutive vertebrae (80% vs 43%, p < 0.01), and the presence of more than five lesions within one vertebra (59% vs 8%, p < 0.05). On fast spin-echo T2-weighted images, signal intensity was as follows: hyperintensity (12% vs 32%, p > 0.05), isoin-tensity (36% vs 3%, p < 0.05), and hypointensity (52% vs 65%, p > 0.05). Paraspinal and epidural masses played little part. CONCLUSION: The salt and pepper infiltration pattern, the presence of more than five lesions within one vertebra, and the involvement of more than three consecutive vertebrae were useful MR findings for differentiation between multiple myeloma and metastasis involving the spine. In most cases, however, it is difficult to distinguish between the two conditions.