Tooth autotransplantation is becoming a predictable method to replace a missing tooth, especially in young patients, with many benefits. This case report presents a 14-year-old male with an unrestorable, decayed mandibular first molar with bifurcation and periapical lesions. After the extraction, the socket was debrided and prepared for an immediate autotransplantation of the immature mandibular third molar. Radiologic and clinical follow‑up for 1 year showed periodontal healing with the absence of any complications despite the autotransplantation into an infected site. Thus, third-molar autotransplantation was a good solution to replace an unrestorable first molar with a satisfactory result. Despite the existence of periradicular lesion, the curettage, debridement, and irrigation were enough to perform successful immediate tooth autotransplantation in this case. (Quintessence Int 2023;54:228–233; doi: 10.3290/j.qi.b3631831)