An infected replanted immature maxillary central incisor with sinus tract in a 7-year-old patient was treated. This clinical report illustrates how an infected immature replanted incisor that underwent conventional root canal therapy still progressed into a radicular cyst formation. After long-term Ca(OH)2 dressing, the tooth was extracted due to traumatic injury. Clinical and radiographic data were collected. The authors inspect the reasons of failure and hope to seek for better treatment methods for similar cases.