How fiber in the diet is related to the development of colon cancer was assessed in a population-based study conducted on 231 cases and 391 controls in Utah between 1979 and 1983. Crude fiber consistently decreased risk associated with colon cancer in both males [odds ratio (OR) = 0.4] and females (OR = 0.5). Dietary fiber, as analyzed by the method of A. S. Bitner, and neutral detergent fiber were not consistently related to colon cancer risk. Of the noncellulose polysaccharides examined, mannose and galactose were protective against cancers in the ascending colon in males (ORs = 0.5 and 0.3, respectively), whereas galactose and uronic acid were protective against cancers in the ascending colon in females (ORs = 0.5). Highest quartiles of intake of fruits and vegetables were also associated with a decreased risk of colon cancer in males (ORs = 0.3 and 0.6, respectively) and in females (ORs = 0.6 and 0.3, respectively) compared with lowest quartile of intake, whereas high intake of grains was not protective.