OBJECTIVE We performed this study in order to evaluate the incidence and characteristics of urolithiasis in patients with malignant hematologic diseases. METHODS Nine hundred one patients who underwent medical treatment for malignant hematologic disease and 40,543 patients who visited the emergency room and without malignant hematologic diseases were included in our study. The patients with malignant hematologic diseases were divided into two groups depending on their primary treatment. Group I included patients with acute and chronic leukemia (AML, ALL, CML, CLL) for which chemotherapy and steroid therapy was necessary, and group II included patients with anaplastic anemia and myelodysplastic syndrome and who had undergone repeated transfusion for treatment. Comparisons were made between the two groups in respect to the incidence of urolithiasis and the stones' radiopacity. RESULTS Twenty nine patients (3.2%) of the 901 malignant hematologic patients were diagnosed with urolithiasis, compared to 575 patients (1.4%) of 40,543 emergency room patients. There was a significant increase of the incidence of urolithiasis in the malignant hematologic group. Compared to the general patients, the patients with malignant hematologic diseases had a higher rate of radiolucent stones (46.6% versus 16.3%, respectively), and the difference was significant. CONCLUSIONS The incidence of urolithiasis for malignant hematologic patients was significantly higher than that for the control group.