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Purpose: To investigate magnetic resonance imaging (MRI) features for differentiating ovarian endometrioid adenocarcinoma (OEC) from high-grade serous adenocarcinoma (HGSC). Materials and methods: Twenty-three patients with 25 OECs and 93 patients with 139 HGSCs confirmed by surgery and pathology underwent conventional MRI and diffusion-weighted imaging (DWI). The MRI features of the tumors, including laterality, size, shape, configuration, signal intensity, ADC value of solid component, enhancement, ascites, synchronous primary cancer (SPC) of the ovary and endometrium, and clinical stage, were evaluated and compared between two groups. Results: The following characteristics were significantly more common for OECs than HGSCs: unilateral (91.3% vs 50.5%, P < 0.001), larger mass (80.0% vs 48.2%, P = 0.005), round or oval shape (64.0% vs 17.3%, P < 0.001), mainly cystic with mural nodules or papillary projections (72.0% vs 18.7%, P < 0.001), cystic component with homogeneous iso- or hyperintensity on T1WI (82.6% vs 4.3%, P < 0.001), moderate enhancement (52.0% vs 26.6%, P = 0.011), no or mild ascites (91.3% vs 57.0%, P = 0.002), and SPC (43.5% vs 4.3%, P < 0.001). The ADC value of the solid component was higher in OECs (0.979 ± 0.197 × 10-3 mm2/s) than in HGSCs (0.820 ± 0.112 × 10-3 mm2/s) (P = 0.002). When a mainly cystic mass with mural nodules or papillary projections was associated with any one of homogeneously iso- or hyperintense cystic component on TIWI, a relatively higher ADC value and SPC, the sensitivity, specificity, accuracy, and positive and negative predictive values for characterizing OEC were 87.0%, 93.5%, 92.2%, 76.9%, and 96.7%, respectively. Conclusions: Conventional MRI combining DWI is helpful for differentiating OECs from HGSCs. [ABSTRACT FROM AUTHOR]