Objective: The aim of this study was to evaluate temperature variation induced by a diode laser in periodontal repair. Background Data: A diode laser operating with medium power can constitute an alternative device for bacterial reduction at periodontal pockets. This procedure will probably avoid any kind of undesirable thermal damage to the irradiated tissues. Methods: The temperature variation induced by a 810-nm diode laserwas investigated in an in vitro study, varying the soft tissue thickness, and in an in vivo study for soft periodontal and bone tissues. The laser powers used were 600 mW, 800 mW, 1.0 W, and 1.2 W, and the light was delivered by a 300-µm fiber. Results: The laser parameters and irradiation time used did not induce a temperature variation high enough to cause thermal irreversible damage to the periodontal tissues investigated. Conclusions: This study contributes to the establishment of thermally safe working parameters of a diode medium power laser.