Multiple spinal epidural metastases; an unexpectedly frequent finding. In a prospective study, patients with known malignant disease who were suspected of having a spinal epidural metastasis, had myelography which was not confined to the clinically suspected site, but included at least the whole lumbar and thoracic spinal canal. Fifty four of the 106 myelograms revealed at least one epidural metastasis. Twelve of these 54 myelograms showed two separate lesions, and four myelograms showed three separate lesions. In all 16 cases with multiple lesions at least one of the lesions was asymptomatic at the time of the diagnosis. It is concluded that multiple spinal epidural metastases are of common occurrence and occur in about one third of the cases. This finding may have important clinical implications. Examination of the spinal canal for epidural metastases should not be confined to the clinically suspected site, but should include as extensive an area as possible of the spinal canal, whatever technique is to be used. 