A survey was undertaken to analyze implants placed in irradiated tissues. It was found that nine centers had placed 188 implants in 24 patients in Japan. Of 118 implants, 39 were in the maxilla, 71 were in the mandible, and 8 were in the orbital region. Seven patients underwent adjunctive hyperbaric oxygen treatment. The treatment decreased implant loss only in the maxilla. (The success rate without hyperbaric oxygen treatment was 62.5%, and that with hyperbaric oxygen treatment was 80.0% for the maxilla.) Implants 7 and 10 mm in length were at a greater risk of being lost than longer implants in the maxilla.