Background. Reduction of saliva secretion is a common side effect following radiotherapy (RT) for cancer of the head and neck region. The aim of this study is to predict the post-RT salivary function for individual patients prior to treatment and to recognise possible differences in individual radiosensitivity. Material and methods. A predictive model for post-RT salivary function was validated for 64 head and neck cancer patients. The input parameters for the model were salivary excretion fraction (sEF) measured by 99mTc-pertechnetate scintigraphy, total stimulated salivary flow and mean absorbed dose for the major salivary glands. SEF values after RT relative to the baseline before RT (rEF) were compared among the patients using the distance ΔrEF between single gland rEF and the corresponding expected value at the dose response curve. Results. A significant correlation (R = 0.86, p = 0.018) was found between the modelled and the measured values of stimulated salivary flow six months after RT. The average prediction error for the saliva flow rate was 6 ml/15 min. A linear relationship between ΔrEF for the left and the right parotid glands was observed both six (R = 0.53) and 12 (R = 0.79) months after RT. The average of absolute values of ΔrEF was 0.20 for parotid glands and 0.22 for submandibular glands. Conclusions. The salivary flow model was validated for 64 patients. The results imply, that one explanation for the discrepancies between the predicted and the measured salivary flow rate values and the common variations found in ΔrEF for the parotid glands may be differences in patients’ individual response to radiation. However, quantitative extraction of individual radiosensitivity would require further studies in order to take it into account in predictive models.