PURPOSE: Despite the burgeoning geriatric population with cancer and the importance of understanding how age may be related to mental adjustment and quality of life so far, differences in coping strategies and psychological harm between the elderly and adults are hardly being taken into account to modify the approach to this population. The aim of this prospective study is to describe the differences in psychological characteristics between older and adult cancer patients and examine dissimilarities in their psychological evolution during adjuvant chemotherapy. METHODS: Adults (18-69 years old) and older patients (≥ 70) with newly diagnosed non-metastatic resected cancer admitted to receive adjuvant chemotherapy were recruited. Patients completed the following questionnaires: mini-mental adjustment to cancer, brief symptom inventory, shared decision-making questionnaire-patient's version, multidimensional scale of perceived social support, EORTC quality-of-life instrument, life orientation test-revised, and satisfaction with life scale. RESULTS: 500 cancer patients (394 adults and 106 older) were evaluated. The impact of the diagnosis was less negative among older patients, with no differences in coping strategies, quality of life, or search for support. Regarding psychological changes from the beginning to the end of the adjuvant treatment, both age groups reported more somatic symptoms, increased psychological difficulty, reduced coping strategies, and a significant decrease in quality of life at the end of postoperative chemotherapy. CONCLUSION: Although there were clear psychological differences between adults and senior cancer patients, their evolution during adjuvant chemotherapy was similar, with deterioration in quality of life and coping. This negative psychological impact of adjuvant chemotherapy should be taken into account when considering interventions.