In order to study the relationship between benign breast changes, a family history of breast cancer and breast cancer, extratumoral breast tissue from 1259 breast-cancer patients in the WHO Collaborative Study of Neoplasia and Contraceptives was classified histologically. The occurrence of ductal hyperplasia, ductal atypia, sclerosing adenosis, adenosis, lobular atypia, lactational metaplasia, cysts, apocrine metaplasia, apocrine hyperplasia and atypia, duct ectasia and the epithelial-stromal ratio was evaluated as absent, mild, moderate or marked, along with registration of the quality and number of slides. Information on occurrence of cancer in the family was available for patients' mothers and grandmothers. Logisticregression analyses showed that the prevalence odds ratios for lactational metaplasia, cysts, duct ectasia and calcification were significantly increased in patients with a family history of breast cancer. Apocrine metaplasia and hyperplasia were not significantly increased. The prevalence rates of ductal atypia (ductal carcinoma in situ and atypical ductal hyperplasia), ductal hyperplasia, sclerosing adenosis, adenosis and high epithelial-stromal ratio did not differ significantly among patients with or without a family history of breast cancer. A family history of other types of cancer did not influence the occurrence of any of the benign components. The findings in the present study are strikingly similar to those in our earlier comparison of extra-tumoral breast tissue in patients from countries with high and low risk of breast cancer. It is reasonable to conclude from this that a history of breast cancer in a woman's mother or grandmother and the factors leading to higher risk of breast cancer in some countries than in others have similar effects on the morphologic evolution of breast cancer through benign and pre-cancerous changes. Int.