Rhinosinusitis is one of the more common diseases encountered in outpatient visits to health care. The objective of this study was to determine the most cost-effective antibiotic treatment for patients with acute (RSA) and chronic rhinosinusitis (RSC) that is available at the Mexican Institute of Social Security (IMSS). Cost-effectiveness analysis of RSA and RSC treatment from an institutional perspective. Effectiveness outcome was defined as the percentage of cure. A decision tree with a Bayesian approach included the following therapeutic alternatives: ciprofloxacin, gatifloxacin, trimetoprim/sulfametoxazol (TMP/SMX), amoxicilin/clavulanic acid (AAC) and clindamicin. Treatment for RSA with AAC showed a mean cost per cured patient of $ 878 pesos. The remaining antibiotics had a higher cost per unit of success, and therefore the results showed that AAC was the best alternative considering this criterion. The therapy that showed a larger percentage of cured patients in RSC was clindamicin; however, the therapeutic alternative with the lowest cost per successful unit was the one based on ciprofloxacin, which dominates gatifloxacin and AAC. The most cost-effective alternative in the antibiotic treatment of patients with RSA was ACC while for RSC it was ciprofloxacin; sensitivity analysis showed the strength of the base study results.