Fifty patients with lumbar spinal disease, 47 of them with disk herniation, were studied preoperatively using both electromyography and computerized tomography (CT), in order to verify the mutual diagnostic significance and accuracy of these techniques. Electromyographic studies provided correct informations regarding the level of the lesion in 41 patients with 1 mistaken level and 8 false negatives, without indicating the nature of involved pathologies. The specific nature of the lesions was correctly indicated by CT studies in 43 patients with 4 incorrect diagnoses and 3 false negatives, without defining the functional loss produced by the lesions. Using electromyography and CT together, first electromyographic studies to establish the spinal level to investigate principally with CT, the diagnostic accuracy can improve because of the decrease of the false negatives.