Background: To date, only few investigations are available regarding the side effects of radiotherapy and the coping of patients with them. In order to determine to which extent the patients’ complaints are subject to personality characteristics, the patients were interviewed; the information on physical and mental strain thus obtained was correlated to the patients’ personality characteristics. Patients and Methods: 91 radiooncological patients were interviewed for physical complaints and impairment of mental state at start, in the middle and at the end of an approximately 6-week course of radiotherapy. The patients (66 females, 25 males) had different diagnoses, but comparable histories and durations of disease (all of them having had surgery as first treatment shortly before). Furthermore, at the beginning of radiotherapy specific personality factors were determined. The correlation between the impairments reported and personality factors was calculated (differentiated for age and sex). Results: We observed a marked correlation between the reported (physical and mental) impairments and an attitude that may be defined as a communicative and social regression and resignation. The extent of impairments quoted was the higher the more patients tended to react to stress situations by social regression and resignation. Conclusions: The results reveal that, on the one hand, a more precise differentiation between objective and subjective side effects is required; on the other hand, complaints not only express a certain way of coping with a situation but also must be seen as the reflection of the physician – patient relationship.