Histological diagnosis of well differentiated endometrioid adenocarcinoma (WDA) has been challenging over the years. Considering the impact of this diagnosis on treatment and follow-up of the patient, in this review, we have discussed and evaluated the most useful of the proposed histological criteria for diagnosis of WDA and its distinction from mimic lesions.Diagnostic criteria for WDA are proposed regarding histologic features predicting the presence of myometrial or endometrial stromal invasion by proliferating glands, or aggressive behavior.Most useful diagnostic histological features in WDA, such as cribriform, labyrinthine, and confluent glandular patterns, and stromal desmoplasia are highlighted. Presence of these features differentiates WDA from mimics and justifies aggressive treatment.