Nasal endoscopy has been practiced by allergists since the early 1980s; however, allergists in general have not embraced endoscopic evaluation of patients with sinus disease, either before or after surgery. Allergists are in a unique position to render medical (as opposed to surgical) care of patients with sinusitis. There has been a growing realization that endoscopy is a valuable procedure for the evaluation and medical treatment of patients with difficult sinusitis. This has resulted in the need for a resource to allow allergists to understand the nature of endoscopic findings in patients with sinusitis, either preoperatively or postoperatively. This article introduces the findings at endoscopy that are common in patients with sinusitis, including those that may be seen after surgery. The findings include perforation of the septum, retained secretions, small surgical ostium caused by postoperative ostial stenosis, previous Caldwell Luc procedure, recirculation of mucus, hyperplastic nasal disease, synechiae, recurrent disease in previously unaffected sinuses, empty nose syndrome, frontal sinus disease, dental disease, and other, more complicated entities.