A critical evaluation revealed no distinct clinical complex of symptoms related to the radiological picture of chronic adhesive arachnoiditis in the lower lumbar sac in 72 patients. In all cases the arachnoiditis was diagnosed by myelography with water soluble contrast media and, in 16 cases, verified by operation and microscopy. The assumed cause of arachnoiditis was, in more than half of the cases, the combination of myelography and operation in close relation, and, in ten cases, a previous operation.