The presence and/or depth of myometrial invasion of endometrial adenocarcinoma has important prognostic and therapeutic implications. Fifteen patients with histologically proven endometrial cancer underwent preoperative evaluation with sonography (US) and magnetic resonance imaging (MRI) to assess depth of invasion. Using criteria of greater than or equal to 50% of myometrial wall involvement as representing deep invasion, and less than 50% as superficial invasion, US was more accurate than MRI in five cases; in three MRI was more accurate than US; both MRI and US were equally accurate in four; neither was accurate in three. Polypoid lesions caused the greatest number of false positive reports of deep invasion with both MRI and US. Preliminary results indicate that US and MRI have promise as preoperative tests to assess the extent of myometrial invasion.