Introduction: Primary lung papillary neoplasms are very rare and less than 30 cases of papillary adenomas have been described. Lung-derived papillary lesions arising in ovarian mature cystic teratoma are extremely rare and, to the best of the authors’ knowledge, only one case has been reported. Herein they report the second case and discuss the differential diagnoses. Case Report: A 32-year-old woman presented with bilateral ovarian mature cystic teratoma (MCT) (“dermoid”). The right side teratoma, very close to the thyroid tissue (struma ovarii), presented a morphologically benign mass, with complex papillary structures and psammoma bodies, which mimicked a thyroid papillary carcinoma (TPC). Immunohistochemistry showed diffuse positive staining with EMA, cytokeratins, and patchy positive staining with TTF1 and surfactant apoprotein A. Thyroglobulin, PAX-8, HMBE1, chromogranin, synaptophysin, CD56, CEA, p63, and BRAF were negative. The work-up for metastasis was negative. Close clinical and instrumental follow-up was decided following consultation with the lung and gynaecological multidisciplinary team. Conclusion: This is the second case of benign appearing, lung-derived papillary neoplasm arising in an ovarian MCT. In view of the clinical context, histological criteria used in lung pathology cannot be applied with confidence in this case. The most appropriate term would be pulmonary-derived papillary adenomatoid proliferation. This novel entity will be useful for pathologists and clinicians in diagnosing and differentiating this very rare disease from other lesions arising in ovarian teratomas.