Background: Patients with breast cancer sometimes present with increased liver enzymes during follow-up period that may be consistent with hepatic steatosis. This effect known as non-alcoholic fatty liver disease may be associated with the malignancy itself, drugs or some other well-known risk factors that may induce steatosis. We studied the influences of primary disease and treatment on steatosis in patients with breast cancer. Materials and methods: There were four groups of patients in our study. Group 1: 40 newly diagnosed, previously untreated breast cancer; Group 2: 45 cases of breast cancer treated with systemic therapy; Group 3: 40 cases of ovarian cancer; Group 4: 40 healthy women. Hepatic steatosis was evaluated by sonography by two radiologist, independently. We also evaluated major risk factors, biochemical findings, and influences of treatment on hepatic steatosis. Results: We detected steatosis in 63%, 72%, 77%, and 48% of patients in groups 1, 2, 3, and 4, respectively. There was a statistically significant difference only between groups 3 and 4 (P = 0.045). However, grade 2 and 3 steatosis were more frequent in breast cancer patients (group 1 and 2), compared with mild steatosis in ovarian cancer patients and healthy women. Although a good correlation was found between tamoxifen use and chemotherapy on development of non-alcoholic fatty liver disease, no association of hepatic steatosis with transaminase levels was found, which might be of help for earlier detection of steatosis. AST/ALT ratio was found to have no impact on the rate of hepatic steatosis, contrary to the literature. Conclusion: Hepatic steatosis, excluding patients with grade 1 steatosis, which may be a normal variant, were more readily detected in patients with breast cancer. This effect was aggravated by use of tamoxifen, but not the chemotherapy. Non-alcoholic fatty liver disease in patients with breast cancer may be associated with the primary tumor itself or some well-known risk factors such as obesity, hyperlipidemia, and diabetes mellitus, which needs to be explored. © Humana Press Inc. 2007.