In dentistry, the endoscope has generally been used to visualize inaccessible areas, e.g., inside root canals or coronal surfaces of teeth; however, it has not been used in periodontally diseased lesions. In this study, a newly designed fine fiberscope (0.8- to 1.0-mm outer diameter) with an irrigation system was used to visualize root surfaces and periodontal tissues affected by periodontal disease. The fiberscope was inserted through fistulas, periodontal pockets, or root furcations in 5 patients to provide clear operational views without the obstruction of blood or soft tissues. The irrigation system of the endoscope effectively allowed differentiation of hard and soft tissues as well as restorative materials. The fiberscope system developed in this study was effective for diagnosis, for enhancing visualization for periodontal surgery, and for treating lesions such as fistulous tracts or furcation lesions.