One hundred patients with lumbosacral adhesive arachnoiditis documented either directly at surgery or by unequivocal myelography served as the basis for this report on the pathologic process. Nomenclature for this disease, involving radiculitis, arachnoiditis, and adhesive arachnoiditis, is proposed. The entity appears not to be rare, as previously thought, but common in patients with severe back and/or leg pain and functional incapacitation due to the failed back surgery syndrome. While true incidence and relationship to a combination of causal factors remains to be accurately documented, the importance of Pantopaque in contributing to this disease process appears to be quite significant.