Introduction. Lophomonas blattarum is a rare cause of bronchopulmonary and sinus infection. This paper presents a rare case of Lophomonas sinusitis. Case Presentation. The patient was a 31-year-old woman who was admitted because of a history of upper respiratory infection and sinusitis. Direct microscopic examination of the sputum and nasal discharge showed large numbers of living Lophomonas blattarum with irregular movement of flagella. The patient was successfully treated by Metronidazole 750 mg t.i.d. for 30 days. Conclusions. This is the first case report of Lophomonas blattarum sinusitis from Iran.