Frozen-section and paraffin section diagnoses were compared in 55 patients with Stage I endometrial adenocarcinoma. In 44 patients (80%), a corresponding depth of myometrial invasion and in 54 (98%) patients the same tumor grade were found. Regarding the depth of myometrial invasion and histologic grade, sensitivity, spesificity, positive and negative predictive values were 70%, 86%, 73%, 83% and 92%, 100%, 100%, 94%, respectively. Concerning myometrial invasion 9% false-positivity and 10% false-negativity rates were noted. The histopathologic characteristics of false-positive and false-negative patients are emphasized because carcinomatous involvement of deeply situated adenomyosis and advanced grade tumors are the main diagnostic pitfalls.