OBJECTIVES: In February 2001, the Ontario Drug Benefit (ODB) Formulary was changed so that most fluoroquinolone (FQ) antibiotics would be reimbursed as Limited Use (LU) or subject to further LU restrictions in response to concerns about increasing rates of resistance to the FQs. This study analyzed the impact of the LU policy on antibiotic resistance, particularly in community acquired pathogens. METHODS: Ontario data from the Canadian Bacterial Surveillance Network aggregated by month between Jan 1, 1998 and June 30, 2002 examines various drug/pathogen combinations for resistance. Streptococcus pneumoniae (4765 isolates) was tested for susceptibility to various drugs while group A Streptococcus (1210 isolates), and Haemophilus influenzae (761 isolates) were tested for susceptibility to a single drug. The effect of the LU policy on the level and rate of change of antibiotic resistance was estimated using time series analysis with ARIMA models, where indicated by autocorrelation, or Poisson regression models where autocorrelation was not present. RESULTS: Resistance rates for S. pneumoniae were in the range of 10-12% for penicillin, erythromycin and trimethoprim sulfamethoxazole (TMP/SMX) and less than 3% for amoxicillin and all three FQs tested. Resistance for group A Streptococcus to erythromycin was about 7% and for H. flu to ampicillin was about 27%. There was a steady increase in resistance rates of S. pneumoniae to amoxicillin and levofloxacin throughout the study period. There was, however, no indication of any decrease in resistance rates associated with the LU policy. CONCLUSIONS: Although no direct cause and effect can be proven with these observational data, there is no evidence that the LU policy to restrict FQs decreased resistance in any of the drug/pathogen combinations tested during the 17 month post-policy period.