Objective. The aims of this study were to compare the diagnostic performance of sonohysterography (SH) with that of magnetic resonance imaging (MRI) in estimation of myometrial invasion and to evaluate the influence of SH on peritoneal cytologic results for patients with endometrial cancer. Methods. Seventy-four patients with endometrial cancer were included. Sonohysterography and MRI were performed before surgery. All patients had complete staging procedures, including peritoneal cytologic analyses. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were determined for SH and MRI. Results. The concordance rates of myometrial invasion for SH and MRI were 82.4% and 81.1%, respectively. The sensitivity, specificity, PPV, and NPV for identification of deep myometrial invasion were 64.7%, 87.7%, 61.1%, and 89.3% on SH and 70.6%, 84.2%, 57.1%, and 90.6% on MRI. Two patients (2.7%) were found to have positive results for malignant cells on peritoneal cytologic analyses. Conclusions. Sonohysterography appears to be a useful preoperative method for predicting myometrial invasion, comparable to MRI.