We investigated the prognostic value and gradation of the T category in N0 nasopharyngeal carcinoma (NPC) patients undergoing magnetic resonance imaging (MRI) and intensity-modulated radiotherapy (IMRT).A total of 749 patients were retrospectively reviewed, and a total of 181 N0 NPC patients were included in this retrospective study. All patients were restaged according to the 7th edition of the American Joint Committee on Cancer staging system. The following endpoints were estimated: overall survival (OS), progression-free survival (PFS), locoregional relapse-free survival (LRFS), and distant metastasis-free survival (DMFS).The 5-year survival rates for T1 to T4 were: OS (97.3%, 100.0%, 86.1%, and 82.8%; P = 0.007), PFS (94.6%, 96.9%, 76.5%, and 76.7%; P = 0.002), LRFS (98.5%, 100.0%, 92.2%, and 86.7%; P < 0.001), and DMFS (97.3%, 96.9%, 85.5%, and 85.7%; P = 0.042), respectively. Pairwise comparisons showed that the OS, PFS, and LRFS rates were significantly poorer in the advanced T categories (T3 and T4) than the early ones (T1 and T2), and no significant differences between T1 and T2, and T3 and T4 were found. In Cox's proportional hazard analysis, T category was found to be an independent prognostic factor only for PFS (P = 0.003). According to the primary tumor extent, we then graded all 181 N0 patients into 3 groups: group 1, early T category (n = 107); group 2, low-risk advanced T category (n = 35); and group 3, high-risk advanced T category (n = 39). The 5-year survival rates for the 3 groups were: OS (98.1%, 94.1%, and 76.3%; P < 0.001), PFS (95.3%, 88.2%, and 66.2%; P < 0.001), LRFS (99.0%, 97.0%, and 83.4%; P < 0.001), and DMFS (97.2%, 91.1%, and 80.4%; P = 0.002). The 5-year OS, PFS, and LRFS rates of group 3 differed significantly from those of groups 1 and 2, and a significant difference was observed in the DMFS rate only between groups 3 and 1. In Cox's proportional hazard analysis, the 3-grade T category was an independent prognostic factor for OS (P = 0.002), PFS (P < 0.001), and LRFS (P = 0.002).The 3-grade T category, using MRI according to the site of invasion, has prognostic value for the outcome of IMRT treatment in N0 NPC, and could aid in developing individualized treatment strategies.