Objective: To compare clinical and sonographic features of benign, borderline, and malignant invasive mucinous ovarian tumors (MOTs). Materials and Methods: Retrospective observational multicenter study comprising 365 women (mean age: 46.1 years) with a histologically confirmed benign, borderline or malignant invasive MOT. Clinical data (patient's age, patient's complaints), tumor markers (CA-125 and CA-19.9), and sonographic data (tumor size, bilaterality, morphology unilocular, multilocular, unilocular-solid, multilocular-solid and solid-, and IOTA color score) were reviewed and compared among these three groups. Women with ultrasound evidence on intra-abdominal disease spread were excluded. Results: Three hundred seventy-eight MOTs (14 women had bilateral lesions) were analyzed. Histologically, 287 tumors were benign, 51 were borderline, and 40 were malignant. No difference in patient's mean age was observed. Women with borderline or invasive tumors were less frequently asymptomatic. Tumors were larger in case of invasive lesions. Borderline and invasive tumors showed solid components and exhibited IOTA color score 3 or 4, more frequently than benign lesions (p < 0.001). However, the authors discovered that 16 out of 51 (31.4%) of borderline tumors and six out of 40 (15.0%) of invasive cancers had no solid components and a color score 1 or 2, and were considered as a benign lesion by the sonologist. On the other hand, 96 out of 287 (33.4%) benign mucinous cystadenoma exhibited solid components and/or a color score of 3 or 4. Conclusions: In spite of statistical differences, the authors observed significant overlapping in ultrasound features among benign, borderline, and invasive ovarian mucinous tumors that renders a difficult accurate preoperative discrimination among these lesions.