We have retrospectively investigated 15 nasopharyngeal carcinoma patients treated at our institution between March 2007 and August 2009. We used simultaneous integrated-boost whole field intensity-modulated radiation therapy (SIB WF-IMRT) to treat the entire planning target volume in the head and neck cancer. All of the SIB WF-IMRT plans were replanned by use of the junctioned intensity modulated radiation therapy (J-IMRT) technique for comparison. The effect on target coverage and sparing of organs at risk, including laryngeal sparing in the optimal SIB WF-IMRT plan was compared with that achieved with use of the J-IMRT technique. The mean larynx dose and standard deviation was 25.2 ± 5.8 Gy for SIB WF-IMRT and 19.8 ± 16.8 Gy for J-IMRT. A comparison between SIB WF-IMRT and the J-IMRT technique demonstrated that the larynx dose was increased in SIB WF-IMRT. However, when the strong dose constraint was applied to the larynx and the pseudo-volume was used for a steep dose fall-off immediately outside the target, the SIB WF-IMRT technique would have led to a larynx dose comparable to that achieved with J-IMRT. Therefore, in our current practice we use the SIB WF-IMRT technique, which does not have the problem of setup error at the match line for treatment of nasopharyngeal carcinoma.