Questionable or unproven methods are used by cancer patients throughout the world. Treatments include drugs, vitamins, herbs, diets, healing, "psychological" treatments, folk medicines, and homeopathy. The exact frequency of questionable methods in cancer is difficult to evaluate because of the variety of methods, some being used as complementary treatments to conventional ones (and often not mentioned by patients) and others, as curative treatment (alternative treatment). In Europe, data are available for the Nordic countries, Switzerland, Germany, Austria, United Kingdom, The Netherlands, France and Italy. High frequencies of use are observed in German-speaking countries (52-65%). In North America, many publications give frequencies of between 7% and 54%. In Mexico, the frequency is 50%, higher than in Argentina (17%). In Australia, 22% have used complementary medicines. In Asia, some data are available from India, Taiwan and Japan. In Tunisia (northern Africa), the results of 59 interviews also show the use of questionable methods among Arabic patients. There is a lack of data from countries in Africa and in Asia. While some products are used all over the world (e.g. mistletoe, vitamins), others are country specific (Moerman diet in The Netherlands). Some traditional medicines are also country specific (e.g., Chinese medicine, Ayurvedic medicine in India). Both alternative and complementary unproven methods are prescribed either according to classical concepts of cancer treatment or according to a new concept of the world and of life.