Introduction: The aim of this study was to evaluate the efficacy of diffusion-weighted images (DWIs) in the differentiation of hydatid cysts (HCs) of the liver., Methods: In this prospective study, 54 patients with 92 HC lesions were evaluated. The mean apparent diffusion coefficient (ADC) values of each lesion were calculated using the ADC maps derived from the DWIs at b-values of 50, 500 and 1000 s/mm(2). We compared the mean ADC values of the different HC types, which had already been classified using the sonographic criteria. A receiver operator curve (ROC) analysis was used for determining the diagnostic performance of the ADC values of the HC types., Results: When the mean ADC values of each type of HC were compared using each of the b-values, no statistically significant differences were obtained between (cystic echinococcosis) CE1 and CE2 or CE3, CE2 and CE3, CE3 and CE4, or CE4 and CE5. In addition, the mean ADC values of CE1 and CE2 were significantly higher than those of CE4 and CE5. For discrimination between types CE1, CE2 and CE3, and types CE4 and CE5, the sensitivity and specificity values were, respectively, 75.9 and 89.5 for the b50 DWI, 87.0 and 86.8 for the b500 DWI, and 75.9 and 89.5 for the b1000 DWI in the ROC analysis., Conclusion: Diffusion-weighted imaging may be useful for providing additional data to determine the type of HC, and for differentiating types CE1, CE2 and CE3 from types CE4 and CE5., (© 2015 The Royal Australian and New Zealand College of Radiologists.)