Breast cancer is the most common malignancy in women, with more than I million cases occurring worldwide annually. Cancer is one of the leading causes of mortality in Turkey; deaths due to breast cancer constitute 24.1% of all carcinoma cases reported among women. We conducted a case-control study of Turkish women with and without breast cancer to investigate the relationships of selected lifestyle and nutritional risk factors with breast cancer risk. Factors were chosen based upon published associations with breast cancer Subjects were women in Izmir Turkey. Cases were 123 women with breast cancer registered with the Department of Oncology. Ege University Hospital, in February through July 2004. The control group included 120 randomly selected women without a breast cancer diagnosis, registered with the Evka-4 Health Care Center and having similar sociodemographic characteristics. Inclusion criteria for participation consisted of 40 yr of age and over and willingness to participate. chi(2) tests and t-tests were used to determine statistical differences between cases and controls based on selected variables. Logistic regression was used to find the association between selected risk factors and breast cancer occurrence. Cases had smoked for more years, their age of first pregnancy was higher and breast cancer occurrence was more common in first-degree relatives such as mothers and sisters of cases compared with controls. Cases were found to have consumed higher amounts of vegetable oil in contrast to controls. These findings are consistent with similar studies conducted in both developed and developing countries.