In 86% of 63 patients with spinal arachnoiditis the localization was lumbosacral, and in 14% it was cervical or thoracic. The most important aetiological factor was the combination of one or more myelographies with one or more operations. It is remarkable that in most patients with lumbosacral arachnoiditis the clinical picture did not show new or typical signs of arachnoiditis, but was the same as before the arachnoiditis had developed. In only 20% of patients with lumbosacral arachnoiditis, and in all patients with cervical or thoracic arachnoiditis, did new signs and symptoms occur concomitantly with and due to the development of the arachnoiditis. The results of this retrospective study suggest that lumbosacral arachnoiditis is a coincidental finding in the majority of cases, without clinical consequences.