A randomized comparative clinical trial was conducted to investigate the possibility of decreasing the duration of treatment of acute otitis media by comparing the clinical out-come and safety of a five-day and a ten-day course of cefprozil. A total of 708 pediatric patients were enrolled in the study, 560 of whom were evaluable for efficacy. Cefprozil was found to be completely effective in 87.1 % of cases after five days of treatment, and in 91.2% after ten days of treatment. Of 19 patients with three or more previous episodes of acute otitis media, ten patients in the ten-day treatment group had a 100% cure rate, while in the five-day group four experienced cure, three improvement, and two failure. A five-day course of treatment with cefprozil can be recommended only if children have no history of recurrent acute otitis media.