Objective To evaluate the adjunctive effect of diode laser irradiation for the treatment of periodontalendodontic combined lesions. Methods 30 cases with periodontal -endodontic combined lesions were selected. All cases were randomly divided into experimental group and control group（n=15）. In the control group, patients were treated with root canal therapy and conservative periodontal treatment（scaling and root planning）, and patients in the experimental group were treated with root canal therapy and conservative periodontal treatment followed by diode laser irradiation. Clinical measurements including pocket probing depth（PPD）, clinical attachment level（CAL）, modified bleeding index（mBI）, periapical index（PAI） were taken before treatment（baseline）. Three and six months after the treatment, the adjunctive effects of diode laser in the treatment of periodontal -endodontic combined lesions were evaluated. Results Three months after the treatment, the average PPD, CAL and mBI levels were reduced significantly in both groups. But the average PPD reduction in the experimental group was significantly greater（P
