Radiotherapy (RT) is a common treatment for head and neck cancers, and frequently causes permanent salivary dysfunction and xerostomia. This 2-year longitudinal study evaluated unstimulated and stimulated parotid flow rates in 11 patients with head and neck cancers who received unilateral neck parotid-sparing RT. The results demonstrated that treated parotid glands had essentially no output up to 2 years post-RT. Alternatively, spared parotid flow rates were indistinguishable from pre-RT values at 1 and 2 years post-RT, and increased slightly over time. Total unstimulated and stimulated parotid flow rates 2 years after completion of RT were similar to pre-RT values, suggesting that spared parotid function may compensate for lost function from treated parotid glands. These results demonstrate that unilateral neck parotid-sparing techniques are effective in preserving contralateral parotid glands up to 2 years after the completion of RT.