The high mortality rate due to ovarian cancer (OVCA) is attributed to the lack of an effective early detection method. Because of the nonspecificity of symptoms at early stage, most of the OVCA cases are detected at late stages. This makes the access to women with early-stage disease problematic and presents a barrier to development and validation of tests for detection of early stage of OVCA in humans. Animal models are used to elucidate disease etiologies and pathogenesis that are difficult to study in humans. Laying hen is the only available animal that develops OVCA spontaneously; however, detailed information on ovarian tumor histology is not available. The goal of this study was to determine the histological features of malignant ovarian tumors in laying hens. A total of 155 young and old (1-5 years of age) laying hens (Gallus domesticus) were selected randomly and evaluated grossly and microscopically for the presence of ovarian tumors. Histological classification of tumors with their stages and grades was determined with reference to those for humans. Similar to humans, all 4 types including serous, endometrioid, mucinous, and clear cell or mixed carcinomas were observed in hen ovarian tumors. Some early neoplastic as well as putative ovarian lesions were also observed. Similarities in histology, metastasis, and stages of hen OVCA to those of humans demonstrate the feasibility of the hen model for additional delineation of the mechanism underlying ovarian carcinogenesis, preclinical testing of new agents for the prevention, and therapy of this disease.