Adult near-infrared spectroscopy is a potential method for observing changes in cerebral oxygenation non-invasively. Access of light to the adult brain requires requires penetration through extracranial tissues; hence the detection of changes in cerebral chromophore concentration can only be achieved by using near-infrared spectroscopy in the reflectance-mode thereby adding variables which are difficult to control. These include the effects of variable anatomy, different intra-optode distances and the presence of an extra- to intracranial collateral blood supply. Although movements of oxygenated haemoglobin concentration following specific cerebral stimuli can be demonstrated, the challenge of separating changes which occur within the extracranial compartment from those occurring in the intracranial compartments remains. Our experience with near-infrared spectroscopy in the three adult clinical scenarios of carotid endarterectomy, head injury and carbon dioxide stress testing will be presented. The influence of extracranial contamination is demonstrated, as are the methods we have developed to help control for extracranial contamination. Provisional experience with spatially resolved spectroscopy technology will also be presented.