Sinusitis is a common finding in avian species; however, it presents unique treatment challenges in ratites. A 6-yr-old male greater rhea (Rhea americana) presented acutely with right infraorbital sinus swelling and chemosis. Oral antibiotics were prescribed based on bacterial culture results with incomplete resolution of clinical signs. A computed tomography scan of the skull demonstrated a mixed-density soft tissue mass with extensive destruction of the right nasal bone, hard palate, maxilla, and frontal bone. The affected tissue was surgically resected and histopathology was consistent with inspissated necrotic tissue. Aerobic culture of the mass grew a multidrug-resistant Escherichia coli and was treated with amikacin. Ten months postsurgery, no further clinical signs were observed. Advanced diagnostic imaging with computed tomography and surgical therapy facilitated complete resolution of this resistant bacterial sinusitis in a species that is not typically amenable to frequent handling and restraint.