Aspects of the nature, causes, prevention and treatment of cancer are examined with emphasis on the value of vitamin C. The view is put forward that routine high intakes of ascorbic acid play a role in cancer by increasing the natural resistance of the patient; resistance of healthy tissues to metastasis by a malignant tumor may be the most important element in cancer progress and outcome. Extension evidence (clinical trials and case histories) supporting a therapeutic role for vitamin C in cancer treatment, especially if begun early, is presented. Increased ascorbate intakes by healthy individuals may also act to prevent the development of cancer. A discussion of the mechanisms of action of vitamin C, including its function in the immune system, provides insight into how the vitamin may work in the prevention and treatment of cancer