Objective.: To describe ultrasound characteristics of adnexal malignancies, i.e., borderline ovarian tumors, primary invasive ovarian epithelial cancer stage 1, primary invasive ovarian epithelial cancer stages 2-4, rare types of malignancy, and metastatic tumors. Methods.: In a prospective international study involving nine European ultrasound centers, 1066 women with a pelvic mass judged to be of adnexal origin underwent transvaginal gray scale and color Doppler ultrasound examination by a skilled examiner before surgery. A standardized examination technique and predefined definitions of ultrasound characteristics were used. Results.: Of 1066 masses, 266 were malignant and are included: 55 ovarian borderline tumors, 144 primary invasive epithelial ovarian cancers(42 stage 1, 102 stages 2-4), 25 rare malignancies, and 42 metastatic tumors. Most(56%) metastatic tumors and most(60%) rare types of tumor were solid and richly vascularized at color Doppler ultrasound examination(on a scale ranging from 1 to 4, color score based on subjective evaluation was 3 or 4 in 88%and 86%, respectively). Borderline ovarian tumors and stage 1 primary invasive ovarian epithelial cancers differed from stages 2-4 primary invasive ovarian epithelial cancers: they were larger(median volume 375 ml and 695 ml vs. 209 ml; P=0.0213 and 0.0001), a larger proportion contained papillary projections(64%and 67%vs. 41%; P=0.0072 and 0.0054), they were more often multilocular cysts without solid components(18%and 14%vs. 2%; P< 0.0017 and 0.0204), but they were less often purely solid(5%and 7%vs. 38%; P≤0.0001 and 0.0005). With increasing degree of invasiveness-from borderline epithelial ovarian tumors via stage 1 invasive epithelial ovarian tumors to stages 2-4 invasive epithelial ovarian tumors-ascites became more common(9%vs. 31%vs. 61%; P=0.0082,< 0.0001, and 0.0017), and, among tumors with solid components(n=179), the proportion of tumor consisting of solid tissue increased(median 2%-10%-34%; P=0.0212, < 0.0001, and 0.0003). Conclusion.: Papillary projections are characteristic of borderline tumors and stage 1 primary invasive epithelial ovarian cancer. A small proportion of solid tissue at ultrasound examination makes a malignant mass more likely to be a borderline tumor or a stage 1 epithelial ovarian cancer than an advanced ovarian cancer, a metastasis, or a rare type of tumor. Objective: To describe ultrasound characteristics of adnexal malignancies, ie, borderline ovarian tumors, primary invasive ovarian epithelial cancer stage 1, primary invasive ovarian epithelial cancer stages 2-4, rare types of malignancy, and metastatic tumors. Methods. international study involving nine European ultrasound centers, 1066 women with a pelvic mass judged to be of adnexal origin underwent transvaginal gray scale and color Doppler ultrasound examination by aperature examiner before surgery. A standardized examination technique and predefined definitions of ultrasound characteristics were used. Results .: Of 1066 masses, 266 were malignant and are included: 55 ovarian borderline tumors, 144 primary invasive epithelial ovarian cancers (42 stage 1, 102 stages 2-4), 25 rare malignancies, and 42 metastatic tumors. Most metastatic tumors and most (60%) rare types of tumors were solid and richly vascularized at color Doppler ultrasound examination (on a scale ranging from 1 to 4, color score based on subjective evaluation was 3 or 4 in 88% and 86% respectively). Borderline ovarian tumors and stage 1 primary invasive ovarian epithelial cancers differed from stages 2-4 primary invasive ovarian epithelial cancers: they a larger proportion contained papillary projections (64% and 67% vs. 41%; P = 0.0072 and 0.0054), they were more often (median volume 375 ml and 695 ml vs. 209 ml; P = 0.0213 and 0.0001) with increasing concentrations of multilocular cysts without solid components (18% and 14% vs. 2%; P <0.0017 and 0.0204), but they were less often purely solid (5% and 7% vs 38%; P≤0.0001 and 0.0005) degree of invasiveness-from borderline epithelial ovarian tumors via stage 1 invasive epithelial ovarian tumors to stages 2-4 invasive epithelial ovarian tumors-ascites became more common (9% vs. 31% vs 61%; P = 0.0082, <0.0001, and 0.0017), and among tumors with solid components (n = 179), the proportion of tumor consisting of solid tissue increased (median 2% -10% -34%; P= 0.0212, <0.0001, and 0.0003). Conclusion .: Papillary projections are characteristic of borderline tumors and stage 1 primary invasive epithelial ovarian cancer. A small proportion of solid tissue at ultrasound examination makes a malignant mass more likely to be borderline tumor or a stage 1 epithelial ovarian cancer than an advanced ovarian cancer, a metastasis, or a rare type of tumor.