Aim: The effect of obesity on subtypes of breast cancer (BC) have been examined in several studies. The aim of this study is to evaluate the association between body mass index (BMI) and BC subtypes. Material and Method: In our institution, 224 BC patients diagnosed between January 2011 and July 2014 were analyzed retrospectively. BMI and hormone-receptor and HER-2 status at the time of diagnosis were recorded. Patients with a BMI >= 25 kg/m2 were grouped as overweight/obese and a BMI < 25 kg/m2 were grouped as thin/normal. Chi-square testing was used to evaluate categorical variables. Results: The mean age of the patients was 53.69 +/- 12.23 years. Fifty-six (25 %) patients had a BMI >= 25 kg/m2, while 168 (75 %) had a BMI >= 25 kg/m2. Ninety-eight (43.8 %) patients were premenopausal, 126 (56.3 %) patients were postmenopausal. The average BMI of the premenopausal group was 27.58 +/- 5.19 in contrast to the average BMI of the postmenopausal group, which was 29.56 +/- 5.26 (p = 0.005). There was a statistically significant increased risk in postmenopausal women who are overweight and obese (Odds ratio: 2.061, 95 % confidence interval: 1.116-3.804, p = 0.02). The patients were divided into two groups according to BMI 25 kg/m2. The groups were compared in the areas of biological subtype classification, degree, histopathological type, staging, lateralism of the BC and presence of metastasis and there were no statistically significant differences in both groups (p = 0,05). Discussion: Weight gain is a preventable risk factor for BC. Therefore we recommend patients pay attention to eating habits and increase physical activity to reduce the risk of BC especially in postmenopausal women.