Many cancer patients use complementary and alternative medicines. Oncologists therefore need to learn more about this subject. Dietary treatments, herbal medicinal products, and various food supplements are currently being promoted as 'cancer cures', but none of these treatments are backed up by convincing clinical evidence. For some interventions, however, the evidence is sufficiently encouraging to warrant further research. Several forms of complementary and alternative medicine play a part in supportive care for cancer patients. The evidence for this approach is still preliminary but, generally speaking, promising. The challenge for the future is to obtain reliable evidence and to identify those approaches that do more good than harm.