Thirty-two cases of lung carcinoma metastatic to the ovary in women 26 to 76 years of age (mean, 47 years) are reported. A history of prior lung carcinoma was documented in 53% of cases (17 of 32), with the ovarian tumor detected at a mean interval of 1 year. In 10 cases (31%), the lung and ovarian tumors occurred synchronously, and in 5 (16%) the ovarian tumor was detected up to 26 months before the lung cancer. Small cell carcinoma was more likely to present with ovarian manifestations than other subtypes. A history of smoking was obtained in 9 cases (28%), but detailed histories were not always available and the figure may be spuriously low. Forty-four percent of the tumors were small cell carcinomas (14 of 32), 34% adenocarcinomas (11 of 32), and 16% large cell carcinomas (5 of 32); there was a single squamous cell carcinoma and one atypical carcinoid. Thirteen percent of cases (4 of 32) had a coexisting primary ovarian tumor. The mean ovarian tumor size was 9.7 cm, and one third of the ovarian metastases were bilateral. Tumor was limited to the lung and one or both ovaries in 13 cases (40%). Morphologic features common to many of the ovarian tumors were multinodular growth, widespread necrosis, and extensive lymphovascular invasion; involvement of the ovarian surface was rare. Attention to these features, to the usual absence of associated typical surface epithelial neoplasia, and to the clinical history enabled the correct diagnosis to be made in the majority of cases without need of special studies. In a minority of cases, immunohistochemical staining for thyroid transcription factor-1 was a useful ancillary marker in the distinction from primary ovarian carcinoma. The differential diagnosis with the primary ovarian tumors most often meriting consideration, including unusual variants of surface epithelial tumors, is discussed.