The discomfort that patients experience during mammography is probably related to a variety of factors, one of which might be the amount of compression used. The authors measured the amount of force applied to the breasts during mammography and the resulting breast thickness in 560 women and correlated these measurements with the patient's subjective impression of the examination. The amount of force applied ranged from 49 to 186.2 N (median, 122.5 N). Breast thickness ranged from 10 to 88 mm (median, 46.5 mm). Forty-seven women (8%) rated the examination as painful (ie, mammography was either "very uncomfortable" or "intolerable"). Logistic regression analysis revealed a highly significant relationship between probability of a painful response and ratio of force to thickness (P = .007). Current guidelines suggest that maximum available force be at least 160 N but not more than 200 N. However, because increasing force is associated with increasing likelihood of pain, technologists should be aware that these recommended maximum limits are not intended to be used routinely for all women. In this study, high-quality mammograms were obtained in a majority of women with forces less than the maximum available level.