The authors recently published data from a prospective cohort study of postmenopausal women (N Engl J Med 1992;326:1323-9) which suggested that a high waist/hip ratio was associated with a significantly increased risk of breast cancer in women with a positive family history of breast cancer. Since families with aggregations of breast and ovarian cancer demonstrate more consistent genetic linkage to markers on chromosome 17q than do families with breast cancer alone, the authors performed additional analyses to examine whether the previously observed associations with waist/hip ratio differed when family history of breast cancer was partitioned according to whether or not ovarian cancer was also present in a close relative. Between 1986 and 1990, 620 incident cases of breast cancer were identified in a cohort of 37,105 postmenopausal Iowa women. A family history of breast cancer in first-degree relatives was associated with a relative risk of 1.34 (95% confidence interval (CI) 1.07-1.69); a family history of both breast cancer and ovarian cancer was associated with a relative risk of 2.36 (95% CI 1.12-4.98). Consistent with the authors' findings after 4 years of follow-up, a high waist/hip ratio (> or = 80th percentile vs. < 80th percentile) was associated with increased risk of breast cancer in the presence of a family history of breast cancer (relative risk (RR) = 2.10, 95% CI 1.43-3.09) but not in the absence of a family history of breast cancer (RR = 1.12). The combination of a high waist/hip ratio with a family history of breast and ovarian cancer was associated with 4.83-fold increased risk (95% CI 1.55-15.1). Neither a family history of breast cancer nor a family history of ovarian cancer was associated with significantly increased risk in the absence of a high waist/hip ratio.