A tribute to Helge Nornes.

This supplement of the Acta Neurochirurgica is dedicated to professor Helge Nornes on the occasion of his retirement. Helge Nornes started his neurosurgical training in Oslo in 1965. In 1980 he was offered the neurosurgical chair of Bern, Switzerland, where he stayed until 1983 when his old university called him back to the chair at the National Hospital in Oslo, a position he filled until he retired last year. The present paper briefly reviews examples of his contributions to neurosurgery and to the understanding of intracranial pathophysiology, including the transcranial doppler, the miniature transducer for intracranial pressure monitoring, his observations on intracranial pressure and internal carotid blood flow during subarachnoid haemorrhage, intracranial arterial blood flow in patients undergoing aneurysm surgery, his studies of the pathophysiology of arteriovenous malformations, the introduction of intraoperative Doppler recordings during surgery for aneurysms and arteriovenous malformations, and his methods for evaluating collateral circulation prior to internal carotid artery occlusion.