The role of dietary calcium as a protective factor in the etiology of colon cancer is reviewed by examining data from ecological and analytical epidemiological studies. Biological evidence that explains the mechanisms whereby calcium intake could alter risk of developing colon cancer is also presented. The data reviewed here in general support the hypothesis that dietary calcium is linked to colon cancer in a protective manner, and that it may be one component in the etiology of colon cancer which alters an individual's risk of developing the disease.