Since 1983 iohexol has been routinely used for myelography in our hospital and 1,650 myelographies have been performed. The first 331 patients with lumbar myelography were included in a follow-up study. Headache was observed in 26 per cent, nausea in 12 per cent and vertigo in 6 per cent of the patients, a frequency very similar to that observed in an earlier study of side effects following spinal puncture. Severe reactions were not seen. Three patients had radicular symptoms and 3 patients had minor mental symptoms possibly caused by the contrast medium. It is concluded that most side effects are related to the spinal puncture and that iohexol probably can be used with safety in out-patients.