Metastatic papillary adenocarcinomas of the ovary are rare compared to primary ovarian papillary serous carcinomas. We report a case of pulmonary papillary adenocarcinoma metastatic to the ovary and show how this tumor can be differentiated immunohistochemically from an ovarian primary. Paraffin blocks of the ovarian tumor were analyzed for carcinoembryonic antigen, CA 125, surfactant, E-cadherin, N-cadherin, and vimentin. These markers are useful in differentiating epithelial tumors of lung versus ovarian origin. The papillary tumor showed expression of carcinoembryonic antigen, surfactant, and E-cadherin, but was negative for CA 125, N-cadherin, and vimentin. These findings support a lung carcinoma metastatic to the ovary.