This study describes the use of complementary therapies (CTs) among breast (women) and prostate cancer patients (men) in Finland. The data were collected using a self-administered postal questionnaire. Responses were received from 216 women (response rate 54.9%) and 190 men (response rate 55.4%). Data analysis was based on descriptive statistics, the chi-square test and Fisher and Wilcoxon tests. Interpretation of the responses to the open-ended questions used the method of content analysis. Half the respondents (women 53%, men 50%) were interested in CTs. Women (59%) had seriously considered using CTs significantly (P = 0.006) more often than men (44%). Among the women and men who had considered the option, CT use was not started because there was not enough scientific evidence (women 56%, men 77%) or because conventional treatments had worked well enough (women 45%, men 70%). Almost one-third of all women (30%) and men (28%) either continued to use or started using CTs after they had fallen ill with cancer. They resorted to CTs in order to restore their hope in the future (women 36%, men 36%) and to do as much as they could for themselves (women 46%, men 29%). The results indicate that cancer patients are interested in CTs and use them quite frequently. This presents a major challenge to official health care: how should cancer patients be supported in the care relationship to make an informed decision about using CTs; what kind of advice should they be given; and how can patients' individual requirements be adequately met in nursing care?