The aim of the study was to assess the relationship between the apparent diffusion coefficient in diffusion-weighted magnetic (DWM) resonance imaging (MRI) and selected morphological parameters of the breast lesions. Diffusion-weighted imaging data and the pathology reports of 160 women treated surgically between January 2011 and March 2015 were analyzed. When classified, 107 invasive carcinomas, 13 pre-invasive carcinomas and 40 benign lesions were identified. The mean apparent diffusion coefficient was significantly lower for invasive carcinomas than benign lesions of the breast (0.87 ±0.02 vs. 1.58 ±0.04; p < 0.001). What is more there was an inverse correlation between value of apparent diffusion coefficient in diffusion-weighted magnetic resonance imaging and the grade of breast carcinomas (p = 0.04).