OBJECTIVE: To analyze associations of short-term exposure to fine particulate matter (diameter = 2.5 microm [PM2.5]), a measurable component of urban pollution, with the event date of fever onset for patients with Kawasaki disease (KD) residing in 7 metropolitan regions. STUDY DESIGN: A case-crossover study design was used. Time trends, seasonality, month, and weekday were controlled for by matching. We assembled PM2.5 exposure measurements from urban monitors and imputed PM2.5 to provide day-to-day temporal variability and resolution for time series indexes of exposures. Selected exposure windows (to 14 days) of PM2.5 were examined. RESULTS: A total of 3009 KD events were included for which the subject resided within a study metropolitan area and the event date occurred during years with available PM2.5. The estimated ORs (with 95% CIs) of an event of KD associated with a 10 microg/m(3) PM2.5 lagged moving average concentration of lagged exposure period (ie, concurrent, preceding day[s]) revealed no evidence of a consistent, statistically significant, positive association between elevated PM2.5 exposure and increased risk of KD. Extended analysis with stratification by city, sex, age, ethnic origin, incomplete or complete clinical manifestations, the presence of coronary aneurysm, and intravenous immunoglobulin resistance did not provide evidence of a consistent, statistically significant, positive association between elevated exposure to PM2.5 and increased risk of KD for any of the strata studied. CONCLUSIONS: This multicity study failed to establish a risk of the event of KD with short-term fine particulate exposure. Our negative findings add to the growing field of environmental epidemiology research of KD.