Quality of life is assessed using standardised general or specific ques­tion­naires. The use of such tools in scientific research makes it possible to determine how the patient functions in specific domains of life, and to measure the overall quality of life and health. A significant step forward in the approach to quality of life assessment is to also take into account factors relating to the patient’s feelings and opinions as well as objective health-related factors. The patient is treated as an entity actively participating in the diagnostic and therapeutic process, whose subjective experiences are important. Research on quality of life assessment constitutes an essential element in the evaluation of the effectiveness of medical technologies. It also represents a new approach to formulating methods of dealing with patients, which is particularly crucial in care for chronically ill patients, including cancer patients.