Photodynamic therapy involves the activation of an exogenously administered, or an endogenously generated, photosensitizer with light to produce localized tissue destruction. It is an attractive, predominantly endoscopic technique for the palliation of advanced upper gastrointestinal cancer and the eradication of early neoplastic and pre-neoplastic lesions. The nature of the biological response allowing safe healing and the exploitation of tissue threshold effects mean that adjacent tissue damage can be minimized. This review used a database of 368 papers. The nature of the photosensitizer is critical to the depth of tissue damage and the risk of adjacent tissue damage and stricture formation. The generation of protoporphyrin IX following administration of 5-aminolaevulinic acid has proved useful for the treatment of high-grade dysplasia in Barrett's oesophagus. A double-blind randomized placebo controlled trial has confirmed that it is a safe and effective method for the ablation of low-grade dysplasia. The treatment of more advanced lesions requires exogenously administered photo-sensitizers. However, recent data indicate that the neoplastic potential remains in some patients and continued follow-up is necessary. Photodynamic therapy can be used to eradicate early neoplasia and palliate advanced cancer, but caution is required before a definitive cure can be claimed.