Oral and pharyngeal cancer is commonly treated with a combination of radiotherapy and surgery. It is a clinical knowledge that patients often experience severe swallowing disorders following treatment. Since surgical sequelae are instantaneous and obvious, little attention has been paid to other concurrent effects of the treatment. To shed light on this subject, the aim of this thesis was twofold (i) to make a retrospective inventory of the sequelae following treatment and (ii) to perform a prospective, inceptive examination at diagnosis, and to follow-up after radiotherapy, six months and 12 months after surgery. The files of ninety-nine patients revealed that following treatment one-third had to use gastric fistulas and more than nine of ten patients had restricted swallowing capacity. Every second patient could only swallow puréed or liquid food. Adequate intra-oral sensation and discrimination ability is essential for bolus preparation and bolus control, for appropriate elicitation of the swallowing reflex and, hence, for the oral phase of swallowing. At the inceptive examination, the prospective part of the study demonstrated intra-oral discrimination ability in patients was equal to that in healthy controls but was impaired six months after treatment and there was no significant improvement after 12 months. It had been expected that the patient’s healthy, non-tumor side would compensate but it did not. An explanation was found when it was revealed that radiotherapy induced a delayed decline in intra-oral sensation. Sensory decline was not demonstrated within a month after radiotherapy but was manifest six months later. Since the radiotherapy field includes the neck, because of the risk for metastasis, it is highly plausible that pharyngeal sensation declines in a manner corresponding to that found intra-orally when the healthy side is irradiated. In accord with this presumption, pharyngeal swallowing function deteriorated in patents with oral tumors. Cineradiographic evaluation of oral and pharyngeal swallowing function disclosed a significant association between the degree of swallowing dysfunction and the degree of sensory decline and with the degree of impairment of shape recognition. Conclusions: Delayed intra-oral sensory decline, found to be induced by radiotherapy, can be expected to appear in the entire radiation field, including the oral cavity and the pharynx, with adverse effect on swallowing. Testing intra-oral sensation close to the last radiotherapy session is not advisable, because sensory decline does not develop immediately after radiotherapy but manifests after six months. Spontaneous sensory rehabilitation cannot be expected after six months. The significant association between degree of swallowing dysfunction and degree of intra-oral sensory decline and impaired discrimination ability must be considered in the quest for functional rehabilitation of patients treated for oral or pharyngeal cancer.