 There is a wealth of literature that supports the use of tissue autofluorescence in the screening and diagnosis of precancers in the lung, uterine cervix, skin and oral cavity. This approach is already in clinical use in the lung and the mechanism of action of tissue autofluorescence has been well described in the cervix. Changes in fluorescence reflect a complex interplay of alterations to fluorophores in the tissue and structural changes in tissue morphology, each associated with progression of the disease. 