A study on the use of fiberscopic examination and multiple biopsy specimens taken from the nasopharynx in the assessment of the extent of nasopharyngeal carcinoma (NPC) involvement inside the nasopharynx found that the involvement often was more extensive than the detected with conventional methods. In the current study, 247 patients with NPC were studied with the use of fiberscopic examination, and multiple biopsy specimens were taken from the superior wall, posterior wall, and lateral wall of the nasopharynx on both sides. It was confirmed that the tumor often involved the nasopharynx extensively. Also, the extent of primary tumor involvement inside the nasopharynx was correlated with the American Joint Committee (AJC) T stage and the degree of paranasopharyngeal extension of the tumor (P = 0.0100 and 0.0009, respectively), as well as with the size of the largest node and the lowest neck level involved by the node in the ipsilateral neck (P = 0.0005 and 0.005, respectively). However, the extent of primary tumor involvement inside the nasopharynx, expressed as either the number of the six standard sites or the number of the AJC subsites that were involved, had no predictive value on the control of the primary tumor (P = 0.3773 and 0.7794, respectively) at a median follow-up time of 27 months. Except when salvage brachytherapy is contemplated for persistent or recurrent NPC, the extent of primary tumor involvement inside the nasopharynx should not be routinely studied.