The accurate prediction of malignancy for a pelvic mass detected on ultrasound allows for appropriate referral to specialised care. IOTA simple rules are one of the best methods but are inconclusive in 25% of cases, where subjective assessment by an expert sonographer is recommended but may not always be available. In the present paper, we evaluate the methods for assessing the nature of a pelvic mass, including IOTA with subjective assessment by expert ultrasound, RMI and ROMA. In particular, we investigate whether ROMA can replace expert ultrasound when IOTA is inconclusive. This prospective study involves one cancer centre and three general units. Women scheduled for an operation for a pelvic mass underwent a pelvic ultrasound pre-operatively. The final histology was obtained from the operative sample. The sensitivity, specificity and accuracy for each method were compared with the McNemar test. Of the 690 women included in the study, 171 (25%) had an inconclusive IOTA. In this group, expert ultrasound was more sensitive in diagnosing a malignant mass compared to ROMA (81% vs. 63%, p = 0.009) with no significant difference in the specificity or accuracy. All assessment methods involving IOTA had similar accuracies and were more accurate than RMI or ROMA alone. In conclusion, when IOTA was inconclusive, assessment by expert ultrasound was more sensitive than ROMA, with similar specificity.