Background and Objective: The aim of this study was to evaluate the efficacy of DWI in differentiation of patients with residual cavity and type 1 hydatid cyst (HC) in the liver. Methods: 32 patients were included. 12 of these patients had type 1 HC and the remainders (n = 20) had postoperative residual cavities. In all patients, axial T2-weighted and DWI images were obtained. An apparent diffusion coefficient (ADC) map of the images was automatically generated and the ADC values were measured on this map for all patients. Mann-Whitney U test was used for comparison of continuous variables between two groups. Results: The mean diameters of type 1 hydatid cyst and residual cavity groups were 83.42 mm, 49.30 mm, respectively (P = 0.001). There were no significant differences in gender and age between the groups (both P > 0.05). The mean ADC values of type 1 hydatid cyst and residual cavity groups were 2.58 +/- 0.13 x 10(-3) s/mm(2), 2.58 +/- 0.16 x 10(-3) s/mm(2), respectively (P = 0.953). Conclusion: DWI might not be suitable to differentiate the postoperative residual cavity from the type 1 hydatid cyst in the liver due to similarity of ADC values between postoperative residual cavity and type 1 hydatid cyst.