We report a case of polypoid endometriosis of the ovary and correlate magnetic resonance (MR) and pathological findings. The endometriosis appeared as multiple polypoid areas along the wall of the ovarian cystic lesion with hyperintensity on T₂-weighted images and slight hyperintensity on diffusion-weighted images. However, the polypoid areas did not yield low apparent diffusion coefficient (ADC) values on ADC map images. These MR findings were similar to the signal intensity of the uterine endometrium, reflecting the presence of abundant endometrial glands.