Objective: The aim of this study was to evaluate the value of DWI and ADC val¬ues in the differential diagnosis of benign and malignant breast masses. Materials and methods: Thirty two patients (age range from 15-68 years, mean 45 years) with histopathologically verified breast masses were included in this study. The patients were exam¬ined with a 1.5 Tesla system using a bilateral phased-array breast coil. Spin-echo echo-planar imaging was used. The images were obtained with a b value of 600 s/mm2. The ADC values were calculated for breast lesions and for normal fibroglandular tissue. Results: The mean ADC was 1.83±0.32×10-3 mm2/s for benign lesions, and 0.71±0.25×10-3 mm2/s for malignant lesions. The thresh¬old ADC value to differentiate benign and malignant lesions was 1.03×10-3 mm2/s. With the ADC ratio (lesion to normal fibroglandular tissue), the threshold was 0.8. The mean ADC ratio was 1.50±0.11 for benign lesions, and 0.6±0.21 for malignant lesions. The ADC values obtained from malignant lesions were statisti¬cally different from those of benign lesions (P<0.001). Conclusion: Diffusion-weighted imaging can aid in the differentiation of benign from malignant breast masses.