Increasing reports of fluoroquinolone-non-susceptible Streptococcus pneumoniae are of clinical concern. We examined the relationship between outpatient fluoroquinolone use and susceptibility of community-acquired S. pneumoniae isolates. Using multivariable general linear modeling, US SENTRY Antimicrobial Surveillance Program and Intercontinental Medical Statistics data (1997-2002) were analyzed to determine the influence of selected patient-, institution-, and geographic region-specific factors, including local fluoroquinolone usage, on the minimum inhibitory concentration (MIC) of levofloxacin against S. pneumoniae. Levofloxacin MIC50, MIC90, and MIC range (n = 384 from 26 hospitals) were 1, 1, and < or =0.5 to >4 microg/mL, respectively. Variables associated with changes in geometric mean MIC included geographical region (P < 0.0001), medical service (P = 0.0002), study year (P = 0.0006), primary diagnosis group (P = 0.02), and 2 interactions (duration of hospital stay before isolate collection by bed capacity, P = 0.06, and levofloxacin use by geographical region, P = 0.08; P < 0.001 when study year was removed from the model). MIC increased with levofloxacin use across all geographical regions, with increases of 54% and 126% in the southwest and west, respectively. In contrast to other fluoroquinolones, increased levofloxacin use, along with other variables, was associated with decreased pneumococcal susceptibility. Given the US environment of increasing pneumococcal resistance, these data may be useful in better understanding factors related to emergence of fluoroquinolone resistance.