Ten psittacine birds (3 African grey parrots [Psittacus erithacus], 3 blue and gold macaws [Ara ararauna], 2 scarlet macaws [Ara macao], a harlequin macaw [Ara ararauna × macao], and a yellow-naped Amazon parrot [Amazona ochrocephala auropalliata]) with histories of chronic sinusitis were referred for evaluation before possible surgical therapy. The duration of clinical signs in these birds ranged from 8 months to 11 years, and response to conventional medical therapy had been poor. Diagnostic procedures performed in each bird included a physical examination, complete blood count, plasma biochemical analysis, survey whole body and skull radiographs, and skull magnetic resonance imaging. In 7 of the 10 birds, a discrete lesion was localized by using magnetic resonance imaging. Six of these 7 birds had surgery performed to remove the lesion. Four granulomas, a mucocele, and a polyp were diagnosed by histopathologic examination. The chronic sinusitis resolved after surgery in 5 birds. Magnetic resonance imaging proved to be an excellent diagnostic tool for examining the avian infraorbital sinus, allowing identification, localization, and characterization of lesions within the sinuses.