The "gold standard" of assessing pathological changes in tissue is currently histopathology. However, the processing of biopsy material and the interpretation of the results inevitably leads to diagnostic delay and the added possibility of taking an unrepresentative sample. Recently, there has been increasing interest in the use of optical spectroscopy systems to be able to provide tissue diagnosis in real-time, non-invasively and in situ. These systems rely on the fact that the optical spectrum derived from any tissue will contain information about the histological and biochemical make up of that tissue. The technique has not only been shown to have a role in the detection of dysplasia and malignancy but also in performing guided biopsies, monitoring of haemoglobin tissue perfusion in free-flaps and therapeutic drug levels during chemo- and photodynamic therapy. The assessment of surgical margins and a role in sentinel node biopsy are also interesting developments. The obvious advantages of being able to accurately diagnose pathology without the need to remove a tissue sample diminish patient trauma as well as having financial implications.