Abstract:  Abstract　Objective: To develop and validate a prognostic model to predict overall survival of patients with Stage IVa-b nasopharyngeal carcinoma ( NPC ) after radiotherapy. Methods: A prognostic prediction model, based on the Nottingham index model, was established to determine the clinical and therapeutic parameters of 535 patients with Stage IVa-b NPC who underwent radiotherapy or chemoradiotherapy in the Cancer Hospital affiliated to Shantou University Medical School from January 2000 to December 2004. The therapeutic efficacy and feasibility of the prognostic prediction model were evaluated. Results: The 1-, 3-, and 5-year overall survival rates of the NPC patients were 90%, 64.4%, and 51.9%, respectively. Univariate and multivariate analyses showed that gender ( G ), age ( A ), Kanorfsky performance status ( K ), N stage ( N ), hemoglobin ( H ), and serum lactate dehydrogenase level ( L ) were independent factors affecting the survival of NPC patients  after radiotherapy. The prognostic prediction model based on these parameters was S=0.397G+0.022A-0.024K+0.203N -0.014H +0.002L. The high and low risks of prognostic index ( PI ) were -1.00 and -1.87, respectively. The 5-year overall survival rate of the patients was 77.7%, 53.9%, and 24.9% for the low-, medium-, and high-risk groups, respectively, stratified by the prognostic prediction model. The differences among these groups were statistically significant ( χ2 = 58.779, P < 0.001 ). Conclusion: A model based on the characteristics of patients has been established. The proposed model provides a high degree of discrimination in predicting the survival of patients with Stage IVa-b NPC  after radiotherapy. This model may be advantageous in selecting the type of treatment for individual patients.