Background: Root canal disinfection is considered critical for achieving successful regenerative endodontic procedures. Photo-activated disinfection is a novel disinfection method that can help to achieve the goal of regenerative endodontics. This article reports the clinical and radiographic results after single visit regenerative endodontics using photo-activated disinfection. Methods: An 8.5-year-old girl complained of fractured upper right central incisor. Pulp necrosis was diagnosed on the basis of clinical findings. The root canal was irrigated with sodium hypochlorite solution (1.5%) followed by saline. Then, the canal was dried with paper points. A combination of a photosensitizer solution and low power laser light were applied. EDTA solution was used as a final irrigant. Bleeding was induced, followed by placement of collagen resorbable matrix and white mineral trioxide aggregate. Two days later, the tooth was sealed and restored with permanent filling. Results: Clinical findings revealed no pain on percussion or palpation tests. Radiographic examination revealed an increase in root length, an increase of apical root thickness and apical closure at the 12-month follow-up period. Conclusion: Regenerative endodontics using photo-activated disinfection achieved successful outcomes in the necrotic immature permanent tooth.