Photodynamic therapy (PDT) is a recently developed treatment involving the use of a photosensitizer and low power light, usually from a laser, to selectively destroy tumor cells. At present, we perform PDT for head and neck cancer using argon or excimer dye lasers with hematoporphyrin derivative as a photosensitizer. This study attempted to assess the utility and safety of PDT and to investigate the long-term outcome. All 24 patients had squamous cell carcinoma: 15 with laryngeal, 5 with lingual or oral, and 4 with pharyngeal cancer and were treated by PDT. Data were obtained from records from February 1988 through April 1995. After PDT, 12 of 15 laryngeal cancer patients were classified as having a complete remission (CR), as were 2 of the 5 lingual or oral and one of the 4 pharyngeal cancer patients. The patients were followed for 8 to 153 months. The longest duration of CR in patients treated by PDT alone was 148 months. Photosensitivity was experienced by all patients, but required no treatment. Liver, kidneys, and bone marrow showed no abnormal values. There were no clinically relevant adverse reactions, and patients with severe complications due to other types of treatment and elderly patients were also treated safely with this therapy.