Abstract: Objective To analyze the failure of helical tomotherapy (TOMO) in treatment of 36 patients with nasopharyngeal carcinoma (NPC). Methods Of the 217 NPC patients admitted to our hospital from September 2007 to August 2012, 36 failed to helical TOMO (including 1 at stage Ⅰ, 5 at stage Ⅱ, 16 at stage Ⅲ, and 14 at stage Ⅳ). Of these 36 patients, 9 received simple radiotherapy and 27 received synchronization radiotherapy. Results The median follow-up time was 27 months (6 - 57 months). The median failure time was 12 months (3 -42 months). Of the 10 patients with local recurrence (including 1 at stage Ⅰ, 1 at stage Ⅱ, 5 at stage Ⅲ, and 3 at stage Ⅳ a), 7 had recurrence in the irradiation field and 3 had recurrence in the irradiation field margin. Three patients had regional recurrence (including 2 at stage Ⅲ and 1 at stage Ⅳ a). Of the 16 patients with distant metastases (including 3 at stage Ⅱ, 7 at stage Ⅲ, and 6 at stage Ⅳ a), 5 had bone metastasis, 5 had liver metastasis, 1 had intramedullary metastasis and 5 had multiple organ metastasis. Seven patients failed to the treatment due to other reasons. Twenty-nine patients died with a death rate of 80.6%. Of these 29 patients, 7 died of local recurrence, 2 died of regional recurrence, 13 died of distant metastasis, 5 died of pharyngeal bleeding with unknown reasons, 1 died of cerebral hernia, and 1 died of systematic failure. Conclusion Recurrence and metastasis are the main reasons for the failure of helical TOMO in treatment of NPC patients. Extension of 5 mm margin of GTV under image guidance is suggested for primary NPC. Radiotherapy in combination with platinum chemotherapy can reduce the failure rate in NPC patients at stage Ⅱ who fail to helical TOMO.