The sinonasal tract is the site of some of the most complex and histologically diverse tumors of the human body. Distinguishing among these lesions on small biopsies can be challenging. This course will review uncommon and common lesions of the sinonasal tract, including infectious conditions and neoplastic diseases. Discussion will focus on the differential diagnosis, appropriate immunohistochemical staining panels, and pathogenesis with an emphasis on molecular evaluation, where appropriate. Participants will enjoy seeing many images, side-by-side comparisons of lesions in the differential diagnosis, and will be taken all the way from distinguishing histologic features to complex molecular analysis.