Complementary/alternative cancer treatments are believed to be prevalent. However, reliable prevalence rates do not exist. The aim of this review was to summarize the existing data on this topic. A series of computerized literature searches was performed to locate all published studies documenting the prevalence of complementary and/or alternative therapy (CAM) use among patients with cancer. A total of 26 surveys from 13 countries, including 4 studies of pediatric patients, was retrieved. The use of CAM therapies in adult populations ranged from 7-64%. The average prevalence across all adult studies was 31.4%. This large degree of variability most likely is due to different understandings of "complementary/alternative medicine" on the part of both investigators and patients. It is likely that the results of the current study reflect the primarily adjunctive use of CAM treatments. Future studies should use a standardized protocol to determine the true prevalence of these therapies more closely.