Ascorbic acid is the single-nutrient supplement most commonly used by cancer patients, although in most cases this takes place without the physician's knowledge or supervision. A comprehensive review of the literature is presented on the impact of ascorbic acid on cancer survival. Findings from 6 uncontrolled studies suggest that ascorbic acid may increase survival, whereas 2 controlled trials have yielded null results. The relative strengths and limitations of these studies are discussed. A turning point occurred with the release of the 2 controlled (null) studies, which influenced many physicians to turn away from nutrition in the care of cancer patients. Controversy about these trials still persists, however, in the alternative cancer community.