BACKGROUND A key requirement for biomimetic regeneration of tissues is a 3D scaffold.The gold standard scaffold for revascularization is the blood clot,however,an adequate blood clot cannot always be achieved in narrow canals or mature roots.Hereby,we document the effects of platelet-rich fibrin(PRF)for the regenerative endodontic treatment(RET)of two immature permanent teeth with necrotic pulps for up to 48 mo.CASES SUMMARY The first patient was a 22-year-old female with history of trauma in tooth#9 with a sinus tract and a large periapical lesion.The second was a 9-year-old male presenting with a badly decayed tooth#14.Both cases were treated with RET and PRF prepared from the patients’blood.PRF and its extract were used as a scaffold for RET.Patients were followed-up to 9 and 48 mo(4 years),respectively.Both patients,were asymptomatic after treatment.At the 9-mo-follow-up of case#1,there was radiographic evidence of periapical bone healing,however,the root apex was still open.In case#2,the roots exhibited apical closure and normal periapical bone architecture at 12-mo follow-up,while no root lengthening was observed.After 48 mo,case#2 showed extensive intracanal calcification in all root canals that complicated conventional root canal treatment.CONCLUSION RET with PRF and its extract could be used in revascularization of immature permanent teeth.However,proper case selection to comply with long-term follow-up is necessary and adverse events such as calcification and canal obliteration should be planned for.