© 2017, H. Lee Moffitt Cancer Center and Research Institute. All rights reserved. Nuclear protein of the testis (NUT) midline carcinoma can present in the head, neck, and mediastinum. In general, it presents in young adult men and has a poor prognosis. We report on a case of NUT midline carcinoma of the mediastinum in a man 27 years of age without any prior malignancy. Due to the location of the tumor, mediastinal lymphoma and germ cell tumor were initially considered; however, immu-nohistochemistry was performed using NUT antibody that revealed it to be NUT midline carcinoma. Although guidelines exist for squamous cell carcinoma of the head, neck, and mediastinum, no such specific guidelines are available for NUT midline carcinoma, which looks morphologically similar to squamous cell carcinoma but behaves more aggressively and carries a poor prognosis.