Introduction: Acute bacterial rinosinusitis is a high prevalence affection, frequently related to viral superior airways infections. Antimicrobial therapy with clarithromycin is well documented in the literature whereas systemic corticotherapy acts as an adjuvant in the inflammation control, by decreasing edema, easing the secretions drainage and the permeability maintenance of the ostia, and favouring, in this way, clinical cure. Aim: This prospective, multicenter, non-comparative study had as primary objective to analyze the symptom evolution of acute bacterial rinosinusitis during the association of systemic prednisolone and clarithromycin. The frequency of adverse events has also been assessed during study period. Methods: Seventy three patients were enrolled, which received 2 tablets of prednisolone 5mg in the morning for 10 days and clarithromycin 500mg once a day for 7 days. The patients could use paracetamol 750mg three times a day if necessary and nasal saline solution as needed. Investigators assessed at D7 and D14 headache intensity, amount and aspect of rhinorrhea and posterior rhinorrhea, aspect of nasal mucosa, nasal obstruction, fever, cough, auricular plenitude, aspect of timpanic membranes and oropharynx, halitosis, odynophagia and fatigue. Results: There was a significant improvement from D7 regarding the aspect of nasal mucosa. Nasal secretion, purulent in the majority of patients at D1 (88,7%), was absent at D7 in 32,4% of the patients (c2 = 20,05 - p<0,001) and in 61,2% Artigo Original 130 Arq Otorrinolaringol, 7 (2), 2003 of the patients at D14 (c2 = 36,21 - p<0,001). Nasofibroscopy was performed at baseline and at the end of the study, whereas all assessed parameters have showed significant changes. Clinical symptoms such as nasal blockage, cough, halitosis, odontalgia, hyposmia, auricular plenitude and fatigue improved significantly with the proposed treatment from D7 ( p< 0,001). Patients who received at least one dose of medication were included in the safety analysis, and, of this total, 38,4% of them reported at least one adverse event, being epigastralgia the most common. Among these events, 42,9% were classified by the investigators as probably related to the study medications. Conclusions: The association of clarithromycin and prednisolone in the treatment of acute bacterial rinosinusitis has proven its efficacy, with a significant improvement of all parameters assessed. Gastrointestinal adverse events were the most frequent ones.