To determine if intensity-modulated radiation therapy (IMRT) improves xerostomia-related quality of life compared with conventional radiation therapy using a validated questionnaire. An Institutional Review Board-approved study of xerostomia quality of life (QOL) was conducted in 210 head and neck cancer patients who were beyond the acute recovery phase (more than 1 year) following radiotherapy. Xerostomia QOL was evaluated with an eight-question xerostomia questionnaire (XQ) developed and validated at the University of Michigan. Five different groups were studied based on extent to which the radiotherapy fields covered the parotid and submandibular glands: a control group consisting of patients whose radiotherapy fields covered only the larynx, ipsilateral fields covering only the ipsilateral parotid and submandibular glands, parallel-opposed fields covering approximately 50% of each parotid gland (called the bilateral partial group), parallel-opposed fields covering more than 90% of all four glands (called the bilateral total group), and parotid-sparing IMRT delivering approximately 50 Gy to the contralateral level II nodes. XQ scores were significantly different (p < 0.05) in each of the four conventional radiotherapy groups, which indicates this instrument is clinically meaningful in this setting. Xerostomia QOL was significantly better in patients treated with IMRT than with conventional parallel-opposed fields even if the conventional radiotherapy fields did not cover the superior portion of the parotid glands (bilateral partial group). The benefit of IMRT was most striking when the mean dose to the contralateral parotid was 26 Gy or less. Specifically, median XQ scores (normalized so that no xerostomia = 0 and the worse xerostomia = 100) were as follows: larynx only group, 4; ipsilateral group, 34; bilateral partial group, 53; bilateral total group, 64; IMRT with mean contralateral parotid dose more than 26 Gy, 44; and IMRT with mean contralateral parotid dose 26 Gy or less, 32. In contrast to the findings of another study on this subject, we found that median XQ scores in any given treatment group were stable over years 1 to 4 following radiotherapy. This study is the first comprehensive evaluation of xerostomia-related QOL in patients who are beyond the acute recovery phase following radiotherapy for head and neck cancer. This study demonstrates that IMRT improves QOL compared to conventional radiotherapy involving parallel-opposed field arrangements, even when the field excludes the superior portion of both parotids. The benefit from using IMRT is most striking when the mean dose to the contralateral parotid is 26 Gy or less