Purpose: To investigate the utility of intravoxel incoherent motion diffusion-weighted MRI (IVIM-DWI) derived diffusion and perfusion parameters in differentiating ocular adnexal lymphoma (OAL) from idiopathic orbital inflammation (IOI), and to assess whether IVIM-DWI provides improved diagnostic performance for the distinction. Method: Twenty-one patients with OAL and 24 patients with IOI underwent IVIM-DWI. Apparent diffusion coefficient (ADC) and IVIM-DWI parameters including true diffusion coefficient (D), pseudo-diffusion coefficient (D*), and perfusion fraction (f) were measured in lesions by two independent radiologists. The MRI parameter differences between OAL and IOI were tested using two-sample t-test. The receiver operating characteristic (ROC) analysis curves were used to determine the diagnostic performance of significant parameters for differentiation between OAL and IOI. Results: The ADC, D, and f were lower in OAL than those in IOI (ADC = 0.78 +/- 0.12 vs. 0.99 +/- 0.16 x 10(-3) mm(2)/s, P<0.001; D = 0.34 +/- 0.15 vs. 0.76 +/- 0.25 x 10(-3) mm(2)/s, P<0.001; f = 0.31 +/- 0.06 vs. 0.41 +/- 0.08 x 100 %, P<0.001). There was no significant difference in D* between OAL and IOI (P = 0.235). The optimal cut-off values of ADC, D, and f in differentiating OAL from IOI were 0.83x10(-3) mm(2)/s, 0.56x10(-3) mm(2)/s, and 0.36 x 100 %, respectively. No significant differences were found in areas under the curve (AUCs) among ADC, D and f (all P>0.05). The combination of D and f provided significantly higher AUC than ADC (AUC = 0.984 vs. 0.838, Z = 2.128, P = 0.033), and had higher sensitivity of 95.24 %, specificity of 95.83 %, and accuracy of 95.56 %. Conclusions: IVIM-DWI is valuable in differentiating OAL from IOI, and D combined f can improve the performance of differential diagnosis.