The aim of this study was to investigate the outcome in 556 patients with locally advanced nasopharyngeal carcinomas treated by radiation therapy alone. We observed 556 patients with stage T3-4 and N0-3 carcinoma who were treated by conventional radiotherapy alone between January and December 1999. The total dose delivered to the nasopharynx was 66-80 Gy over 6.5-8 weeks and to the neck lymph nodes 60-70 Gy over 6-7 weeks. The 5-year actuarial overall survival rate (OS) reached 66.41%. The OS was higher among stage T3 patients than among stage T4 patients (69.12% vs 58.96%, p = 0.0359). Among patients with stage N0, N1, N2 and N3 disease, the OS was 73.98%, 65.96%, 57.58% and 29.39%, respectively (p = 0.0009). Differences in disease-free survival, locoregional control rate and metastasis-free survival rate among each N stage were statistically significant, although this was not true of differences between stage T3 and T4 disease. Multivariate analysis showed that gender, age, T stage and N stage were significant prognostic factors for 5-year overall survival, disease-free survival, locoregional control and metastasis-free survival. We found that N stage is the dominant prognostic indicator for patients with locally advanced nasopharyngeal carcinoma receiving conventional radiation therapy alone, and that T stage was only a secondary correlative factor.