This systematic review aimed to estimate the prevalence of use of complementary and alternative medicine (CAM) in the UK. Five databases were searched for English language, peer-reviewed surveys published between 1 January 2000 and 7 October 2011. In addition, relevant book chapters and files from our own departmental records were searched by hand. Eighty-nine surveys were included, with a total of 97,222 participants. Most studies were of poor methodological quality. Across surveys on CAM in general, the average one-year prevalence of use of CAM was 41.1% and the average lifetime prevalence was 51.8%. In methodologically sound surveys, the equivalent rates were 26.3% and 44%, respectively. In surveys with response rates >70%, average one-year prevalence was nearly threefold lower than in surveys with response rates between 21% and 50%. Herbal medicine was the most popular CAM, followed by homeopathy, aromatherapy, massage and reflexology. Many patients and consumers in the UK use CAM; healthcare professionals should therefore responsibly advise their patients about the use of CAM.