Photodynamic therapy (PDT) is a new modality of cancer treatment. It consists of intravenously injecting a patient with a photosensitizing agent and, when this agent has accumulated in tumor cells, decomposing it by exposure to red light produced by an argon dye laser. Toxic compounds produced in this reaction then destroy the malignant cells, while normal tissue is not significantly affected. Most clinical experience with PDT has been gained in the treatment of lung cancer, cancer of the urinary bladder and malignancies of the head and neck region. In gastroenterology, esophageal, gastric and colonic tumors have clinically been treated with PDT. This paper is to review the current use of PDT in the treatment of gastrointestinal tumors.