The purpose of this study was to explore the views and experiences of adult cancer patients about patient participation in care and decision making and the preconditions for this participation. The data were collected by means of focused interviews; in addition the patients completed depression and problem-solving instruments. The sample comprised 34 cancer patients from the haematological and oncological wards of one university hospital in Finland. The results revealed considerable variation in the patients' views on their participation in care and decision making. Some of the patients understood participation either in terms of contributing to the decision making or in terms of expressing their views on treatment options. Some considered that their participation in care was impossible. Patient participation in care and decision making was promoted by good health, access to information, assertiveness, good interactive relationships with nurses and physicians, and encouragement by nurses and physicians to participate. Factors restricting such patient participation were poor health, ignorance, anxiety, age, time pressures of staff, lack of time, high staff turnover and poor interactive relationships. With regard to participation in medical decision making, the patients were divided into three groups: (1) active participants (n = 7), (2) patients giving active consent (n = 9), and (3) patients giving passive consent to medical decisions (n = 18).