Objectives. Taylor's theory of cognitive adaptation proposes that adjustment depends on the ability to sustain and modify illusions (i.e. unrealistic optimism, exaggerated perceptions of control, and self-aggrandizement) that buffer against threats but also against possible future setbacks. Because the question of whether cancer patients show these illusions has received little attention, the present study compared patients' perceptions of optimism, control, and self-esteem at different stages of the cancer process with that of healthy references. The effects of these perceptions on psychological distress were also assessed. Design. The present study has a longitudinal design. Including a group of healthy references enabled us to draw more firm conclusions about the effect of cancer upon cognitive perceptions. Methods. The participants were 67 cancer patients and 50 healthy references. Patients filled out questionnaires prior to their first radiotherapy (T1), at 2 weeks (T2), and at 3 months (T3) after completing radiotherapy. Healthy references were assessed at similar intervals. Results. T tests revealed that patients experienced significantly higher levels of optimism and self-esteem than the healthy reference group. Concerning control, no group differences were found. Importantly, regression analyses showed that lower levels of optimism and control at T1 were predictive of feelings of anxiety at T3. Lower perceived control also predicted depressive symptoms. Conclusion. Results support the theory of cognitive adaptation in that patients are indeed able to respond to cancer with high levels of optimism and self-esteem and that lower levels of optimism and control are predictive of psychological distress.