Evolution of bacterial resistance shortens antibiotic treatment in ENT infections. The efficacy and tolerance of amoxicillin-clavulanate (ACA), with and without associated short steroid therapy, was evaluated in acute sinusitis of adults at a dosage of 1.5 g/d for 5 d vs. 10 d. This multicentre, randomized, double-blind, placebo-controlled study included 433 patients, 417 of whom were suitable for intent-to-treat (ITT) analysis. The therapeutic success rate in the ITT population, assessed according to strict clinical and radiological criteria, was respectively, 80% and 85% in the 5-d and 10-d treatment groups. Due to the statistical risks that were evidenced, the 2 durations of treatment could not be considered equivalent. The analysis of medical history shows that some risk factors (recurrence of sinusitis, previous surgical sinus drainage) seem to promote therapeutic failure and that 5-d treatment is inappropriate in these patients. The persistence of therapeutic success on day 30 was not influenced by the initial duration of treatment. The efficacy and good tolerance of ACA in acute sinusitis in adults were confirmed. Further studies will be needed to define the indications of short treatments better, which seem to be indicated in the absence of specific risk factors.