Five patients with arachnoidal diverticula after lumbar operations are reported. Myelography was performed in all cases, spinal computed tomography scanning in three; three patients underwent surgical treatment with good clinical results. Arachnoidal diverticula are a rare complication of operations on the lumbar spine. Spinal computed tomography scanning is very useful, especially in the investigation of large diverticula and in the radiologic visualization of the arachnoidal stalk. Surgical treatment, which is required in symptomatic cases, results in remission of pain and prevents neurological complications.