Background/Aim: Breast cancer is the most common type of cancer among women around the world and the leading cause of cancer-related death among women. The knowledge about modifiable risk factors, such as diet, can be an acceptable, cheap and non-pharmacological prevention tool. The aim of this study was to investigate the association between dietary fat, dietary fatty acids, fish intake, and breast cancer in women. Patients and Methods: A case-control study was designed. A total of 201 consecutive, newly diagnosed, polish female cancer patients (mean age: 58 years) and 201 one-to-one age-matched controls were enrolled. A standardised questionnaire assessing various sociodemographic, clinical, lifestyle, and dietary characteristics was applied via face-to-face interviews. Detailed dietary intake information was assessed using a validated Food Frequency Questionnaire. Odds ratios (OR) and 95% confidence intervals (95%CI) were obtained using multiple unconditional logistic regression models controlling for nondietary and dietary potential confounders. Results: Consumption of polyunsaturated fats (PUFA) over 10% of total energy intake was associated with a significantly lower risk of breast cancer compared to low intake of PUFA (OR=0.4, 95%CI=0.19-0.85). Low (<0.2) omega-3/ omega-6 ratio (OR=2.04, 95%CI=0.996-4.17), fish consumption less than once every six months (OR=3.37, 95%CI=1.57-7.23) and being overweight (OR=2.07, 95%CI=1.3-3.3) were associated with increased risk of breast cancer. Residents of rural areas had a significantly higher risk compared to women from urban areas (OR=1.8, 95%CI=1.06-3.03). Conclusion: High intake of PUFA can decrease the risk of breast cancer, while the low omega-3/omega-6 ratio increases the risk. In addition, overweight state, eliminating fish from the diet and living in rural areas can also increase the risk of breast cancer. Breast cancer is the most common type of cancer among women around the world and the leading cause of cancerrelated death among women. In 2018, 2.1 million new cases were diagnosed worldwide, while in the same year breast cancer was the cause of approximately 627 thousand deaths (1-3). In Poland the number of newly registered cases is constantly growing (4). Every year 18 thousand women are diagnosed with breast cancer, which accounts for 22% of all types of cancer among Polish women (5, 6). While known risk factors for breast cancer, such as: age over 40 years, positive family history, early menstruation, late menopause, late age of first pregnancy (after the age of 35 years), duration of breastfeeding, and Caucasian race (7, 8) are basically unmodifiable, the knowledge of nutritional recommendations and the awareness that the diet has an impact on the risk of developing this type of cancer (7, 9) may be harbingers of a new primary prevention system. Many studies have drawn special attention to dietary fat and fatty acids (10-14); however, they do not provide a definitive answer to the question of the role of fat in the aetiology of breast cancer. The wester...