The bacteriological and clinical efficacy and the safety of gatifloxacin for the treatment of non-complicated acute rhinosinusitis was evaluated in 49 adult patients in an open-label multicenter study in Brazil. Patients under age 18, or with associated systemic diseases, were excluded. Diagnosis was based on symptoms, otorhinolaryngological examination, and X-rays of the sinus. At the first visit, all patients were treated with a single daily dose of 400 mg gatifloxacin for 10 days. Middle nasal meatus secretion was collected and sent for culture before and after treatment. Patients were all reevaluated at days 3 to 5; days + 1 to + 5 and 18 to 25 days + 7 to + 14 . Ninety three percent of the patients were considered clinically cured at the end of the treatment. The most frequent bacteria isolated were Haemophilus influenzae, Streptococcus pneumoniae and Moraxella catarrhalis, and at the end of the treatment, presumed bacteriological eradication was observed in almost all patients. Adverse effects were observed in 19 of the cases, mostly mild and self limiting, including diarrhea, abdominal pain, nausea and vomiting. Treatment had to be interrupted in two cases. Gatifloxacin was found to be efficacious and safe for the treatment of acute rhinosinusitis in adults.