Objective – to compare the diagnostic efficiency of whole-body diffusion-weighted magnetic resonance imaging (DW-MRI) and positron emission tomography combined with computed tomography (PET/CT) in the staging of lymphomas.Material and methods. The prospective study enrolled 92 adult patients with Hodgkin's lymphoma or non-Hodgkin's lymphoma. Before treatment, all the patients underwent whole-body DW-MRI and PET/CT. The techniques were compared for their efficiency in diagnosing damage to lymph nodes (LNs) and organs and in determining the stage of lymphoma.Results. The sensitivity, specificity, and accuracy of DW-MRI in diagnosing a lesion in the enlarged LNs were 98.2%, 99.9%, and 99.3%, respectively; those of PET/CT were 99.4%, 100.0%, and 99.8%. ROC analysis showed that the efficiency of the techniques in diagnosing a lesion in the enlarged LNs did not differ (p>0.06). The sensitivity of DW-MRI and PET/CT in diagnosing a lesion in the unenlarged LNs was 77.8% and 88.1%, respectively (p<0.001). The sensitivity, specificity, and accuracy of DW-MRI in diagnosing lung damage were 73.3%, 98.7%, 94.6%; those of PET/CT were 86.7%, 98.7%, and 96.7%; those for the spleen were 54.8%, 98.3%, 83.3% and 100.0%, 100.0%, 100.0%; those for bone marrow (BM) were 87.1%, 96.4%, 93.0% and 64.5%, 87.3%, 79.1%,; those for all organs were 72.9%, 98.1%, 91.4% and 80.0%, 96.6%, 92.2%. The ROC analysis indicated that the efficiency of the techniques in diagnosing a lesion in the lung did not differ (p>0.3), that of PET/CT for the spleen was higher (p <0.0001); that of DW-MRI for BM was higher (p<0.0008); that for all organs did not differ (p>0.35). DW-MRI and PET/CT could determine the correct stage of lymphoma in the same number of patients (86%). The new lymphoma staging algorithm involving whole-body DW-MRI in all patients, PET/CT, and BM biopsies according to the established indications made it possible to determine the correct stage of lymphoma in 95% of patients.Conclusion. Whole-body DW-MRI has comparable efficiency to PET/CT in the staging of lymphoma. The new lymphoma staging algorithm based on whole-body DW-MRI is superior to PET/CT and PET/CT with BM biopsy.