&NA;The findings of a partly prospective case control study of chronic fissue‐in‐ano conducted in two Danish outpatient clinics are reported. One hundred seventy‐four patients with chronic fissure‐in‐ano were matched by age and sex to outpatients from the same community suffering from benign skin tumors. All subjects were interviewed regarding diet, beverage consumption, occupational exposures, and medical and surgical history. Significantly decreased risks were associated with frequent consumption of raw fruits, vegetables, and whole‐grain bread, and significantly increased risks were associated with frequent consumption of white bread, sauces thickened with roux, and bacon or sausages. Risk ratios for consumption of coffee, tea, and alcohol were not significantly different. No statistical associations were found with particular occupational exposures. However, a history of previous anal surgery was reported significantly more often for cases than for controls. Current evidence indicates that anal fissure is likely to result at least partly from an inappropriate diet and that dietary manipulations might reduce the incidence of fissure‐in‐ano.