Objective: Thyroid transcription factor-1 (TTF-1) immunoexpression is frequently determined in small-cell lung carcinomas, as well as primary lung adenocarcinomas. While dealing with metastatic carcinomas, TTF-1 immunoexpression is a significant indicator of primary lung carcinomas. Recent studies have revealed that TTF-1 immunoexpression is also defined in non-lung cancers, such as squamous cell carcinomas of different sites and certain neuroendocrine tumors. The verified data obtained from these studies indicate that a straightforward diagnosis of primary lung carcinoma in cases with positive TTF-1 immunoexpression can cause diagnostic contradictions. The aim of our study is to investigate the immunoexpression status of TTF-1 in common non-lung tumors.