The causes, diagnostic features, and therapy of chronic spinal arachnoiditis are reviewed. Two unexpected results from attempted epidural injections (one of lignocaine and clonidine, and one of lignocaine, clonidine, and morphine) in patients with this condition are described. The anatomical abnormalities of the epidural and subarachnoid spaces in such patients and the consequent unpredictable and potentially dangerous results that may follow drug injection into these spaces are discussed.