The efficacy of routine two-dimensional radiotherapy for primary nasopharyngeal carcinoma (NPC) is dissatisfied, while three-dimensional conformal radiotherapy (3-D CRT) can optimize irradiation dose distribution. This study was to explore the efficacy of 3-D CRT on NPC, and investigate dosimetric factors of locoregional failure. Records of 87 patients with primary NPC, treated with 3-D CRT between Feb. 2001 and Apr. 2004, were retrospectively reviewed. Dosimetric analysis was performed on the patients with locoregional relapse. Of the 87 patients, 5 (5.7%) had local failure, and 2 (2.3%) had regional failure. The overall 3-year locoregional control rate was 90.2%. The 3-year local control rates for stages T1, T2, T3, and T4 patients were 95.0%, 97.0%, 80.1%, and 100%, respectively. Five cases (71%) were marginal or outside failures of the irradiation fields. The occurrence rate of grade 3-4 late complications of the 62 patients progress-freely survived over 12 months was 9.7%. The 3-year overall survival rate and progress-freely survival rate were 88.2% and 80.3%, respectively. The 3-year survival rates were significantly higher in the patients at stages I, II, and III ('92 Fuzhou staging) than in the patients at stage IVa (100%, 100%, 84.7% vs. 47.5%, P<0.001). Increased locoregional control rate and reduced occurrence of grade 3-4 late complications of primary NPC could be achieved by 3-D CRT through careful delineation of target volumes and design of irradiation fields. Missing of target volumes is a reason of local relapse.