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 I 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 I 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.