This report describes 3 successful single-visit regenerative endodontic therapy cases using platelet-rich plasma (PRP) and Biodentine (Septodont, Saint Maurdes Fossés, France) for 3 immature mandibular molar teeth, all with necrotic pulp, in 2 children aged 8 years and 1 aged 9 years. Three teeth were separately diagnosed as having a necrotic pulp. After preparation of the access cavity under rubber dam isolation, the necrotic pulp was removed, and each canal was irrigated with 2.5% sodium hypochlorite, sterile saline, and 17% EDTA solutions. Freshly prepared PRP was injected into each canal up to the cementoenamel junction, and Biodentine was placed directly over the PRP clot. Each access cavity was then restored with composite resin. Follow-up clinical examinations revealed negative responses to cold and electric pulp tests. None of the treated teeth were sensitive to percussion or palpation. Radiographic examination showed continued thickening of root canal walls and apical closure of the root apex of each tooth. Single-visit regenerative endodontic therapy can be considered in necrotic and asymptomatic immature permanent teeth. PRP and Biodentine may serve as scaffold and barrier materials in regenerative endodontic procedures.