Purpose: To investigate the sonographic characteristics of hemorrhagic ovarian cysts (HOC) and to avoid unnecessary surgery. Methods: 113 cases of suspected HOC underwent sonographic and clinical follow-up for three months. Results: 104 cases were clinically diagnosed with HOC as the masses disappeared naturally. The mean length of the greatest diameter was 5.12 ± 1.33 cm, and the mean period of disappearance was 3.5 ± 2.4 weeks. There were four patterns of the image: 21 cases (20.2%) showed a diffused dense echo pattern, 25 cases (24.0%) displayed a mixed pattern, 30 cases (28.8%) expressed a sponge-like pattern and 28 cases (27.0%) exhibited a cystic pattern. Ring blood flow with high velocity and low resistance was detected in 41 cases (40%) and there was no internal blood flow. Conclusion: HOC showed characteristic features on sonography, which provided useful information to differentiate HOC from ovarian tumors.