This study was performed in order to report the clinical features of internal resorption cases and evaluate their prognosis after endodontic treatment. Twenty-seven patients with 28 teeth with internal resorption were referred to our clinic and 20 teeth were treated endodontically. Sixteen teeth had non-perforating internal resorption and were treated by conventional root canal therapy. The remaining 4 teeth had perforating internal resorption and were initially treated by remineralization therapy with calcium hydroxide. The teeth treated by conventional root canal therapy showed clinical and radiographic evidence of healing. However, the remineralization therapy was successful in only one case. The three failed cases were subsequently treated by endodontic surgery. The surgical therapy was unsuccessful in one case due to extensive loss of marginal alveolar bone and increased tooth mobility.