The associations between alcohol and colon and rectal cancers were examined in the Iowa Women's Health Study. In January 1986, 41 837 postmenopausal women, aged 55-69, completed a questionnaire including usual alcohol intake and other information. Through December 1990, 237 incident colon and 75 rectal cancer cases occurred. Mantel-Haenszel age-adjusted relative risks (RR) and 95% confidence intervals (CI) for consumers of < 4.0 and > or = 4.0 g of alcohol per day compared to abstainers were 1.07 (0.61-1.89) and 1.27 (0.72-2.24) (P for trend = 0.46) for rectal cancer. Alcohol intake was inversely associated with distal colon cancer (RR for < 4.0 and > or = 4.0 g of alcohol per day were 0.64 and 0.69 respectively, P for trend = 0.04), which was specific to wine; however, no association was observed with proximal colon cancer (P for trend = 0.94). This is the only report of an inverse association between alcohol and colon cancer in women. Because gut physiology and alcohol metabolism differ between men and women, more research on the association between alcohol and colon cancer in women only, is warranted.