Frequency of strenuous activity during ages 14-22 was ascertained retrospectively from 536 Wisconsin women with newly reported diagnoses of colon cancer and 2315 controls randomly selected from Wisconsin driver's license and Medicare beneficiary lists. Thirty-five % of cases and 34% of controls reported strenuous activity during this period of early adulthood. After adjusting for age, family history of large bowel cancer, history of screening sigmoidoscopy, and body mass index in logistic regression models, women who reported any strenuous activity were at a similar risk of colon cancer as women who did not report activity [odds ratio (OR), 1.02; 95% confidence interval (CI), 0.82-1.27); no significant decrease in risk was seen with increase in frequency of activity (P for trend = 0.84). Results were similar for the right and left colon subsites. These data suggest that early adulthood physical activity may not confer the same protective effect that has been observed with recent physical activity.