The aim of this study was to analyze the behavior of cancer patients. This survey-based study involved 145 oncological patients and was conducted from July to November 2018. It was performed using an author's questionnaire and three standardized tools: the mini-Mental Adjustment to Cancer Scale, the Acceptance of Illness Scale, and the Coping Inventory for Stressful Situations. The acceptance of illness was at a medium level. Patients who had been ill for longer time periods coped with stress better (p < 0.071) and showed better mental adjustment (p < 0.05 for Positive Redefinition, and p < 0.08 for Fighting Spirit). Patients with benign tumors focused on emotions (p < 0.001) and avoidance (p < 0.005) and were preoccupied with anxiety (p < 0.05). Longer treatment time was associated with a higher ability to cope with stress (p < 0.05). Patients receiving support were characterized by Anxious Preoccupation attitude (p < 0.1), and those who had not got it by Fighting Spirit (p < 01). Cancer patients have problems coping with new circumstances. They need support and help to understand and accept their situation.