OBJECTIVES: The aim is to determine if there are any ultrasound features of papillations or of the cyst wall that can discriminate between benign and malignant unilocular-solid cysts with papillations but no other solid components. METHODS: Patients with an adnexal lesion described at ultrasonography as unilocular-solid with papillations but no other solid components were identified from the International Ovarian Tumor Analysis (IOTA) database derived from seven ultrasound centers. All had undergone transvaginal ultrasonography between 1999 and 2012 by an experienced examiner following the IOTA research protocol. Information on four ultrasound features of papillations had been collected prospectively. Information on a further seven ultrasound features was collected retrospectively from electronic or paper ultrasound images of good quality. The histological diagnosis of the surgically removed adnexal lesion was the gold standard. RESULTS: Of 204 masses included, 131 (64%) were benign, 42 (20.5%) were borderline tumors, 31 (15%) primary invasive and one (0.5%) was a metastasis. Multivariate logistic regression analysis showed the following ultrasound features to be independently associated with malignancy: the height of the largest papillation, blood flow in papillations, papillation confluence or papillation dissemination, and shadows behind papillations. Shadows decreased the odds of malignancy, the other features increased them. CONCLUSION: We have identified ultrasound features that can help discriminate between benign and malignant unilocular-solid cysts with papillations but no other solid components. Our results need to be confirmed in prospective studies.