BACKGROUND The specificity of conventional magnetic resonance (MR) imaging is lower than its high sensitivity. Diffusion-weighted imaging (DWI), based on alterations in the microscopic motion of water molecules, promises improved specificity for breast MR imaging. In this study, we aimed to determine the diagnostic potential of DWI to differentiate between benign and malignant breast lesions and normal breast tissue. METHODS Dynamic contrast-enhanced breast MR imaging and DWI were applied to 108 women. Apparent diffusion coefficient (ADC) values were obtained for normal breast tissue (n = 183), benign lesions (n = 66) and malignant lesions (n = 58). The results were compared with the patients' final diagnoses. RESULTS Mean ADC values for benign and malignant breast lesions were 1.04 × 10-3 ± 0.29 × 10-3 mm2/s and 2.00 × 10-3 ± 0.55 × 10-3 mm2/s, respectively (p = 0.001, Student's t-test), while that for normal breast tissue was 1.78 × 10-3 ± 0.33 × 10-3 mm2/s. With a cut-off value of 1.46 × 10-3 mm2/s for ADC in receiver operating characteristic analysis, 95% sensitivity and 85% specificity were achieved for differentiating between benign and malignant lesions. CONCLUSIONS DWI of the breast can help differentiate benign and malignant breast lesions from normal breast tissue. DWI, which can be easily introduced into standard breast MR imaging protocols without increasing imaging times, promises to increase the accuracy of breast MR imaging without contrast media. However, its clinical value will depend on the standardisation of b-values and other technical parameters in larger future study series.