Functional endoscopic sinus surgery (FESS) is well established as the surgical paradigm of choice for management of medically refractory chronic rhinosinusitis (CRS). Robust data has demonstrated efficacy with symptom relief and endoscopic control of the underlying disease process. However, an important subset of patients may continue to suffer from persistent symptoms with ongoing infection and inflammation despite previous surgery and appropriate medical therapy. Optimal evaluation and management of CRS refractory to previous treatment remains an important clinical challenge in otolaryngology. The focus of this course is to outline a systematic, rationale approach to diagnostic evaluation for the failed FESS patient. Common surgical issues contributing to failure, such as maxillary recirculation, incomplete surgery, and synechia formation will be reviewed. The role of extended approaches, including medial maxillectomy and endoscopic modified Lothrop, for enhanced topical access will be discussed. The medical management strategy for refractory CRS, including the role of cultures, oral and topical antibiotics, standard and off-label steroid therapies, and ASA desensitization will be elucidated. The emerging role of new anti-inflammatory therapies, including biologic therapeutics, into the treatment strategy will the outlined. Potential benefits and risks associated with common medical therapies will be reviewed. The role of surgical decision making in this patient population will also be reviewed, including the impact of surgery on long-term success of medical therapy. Cases will be incorporated into the presentations to provide practical pearls to the practitioners to elevate the care of this difficult patient group. The expert series will be delivered by internationally recognized rhinologists with referral based clinical practices focused on management of FESS failures.