Thimerosal as a preservative (in all but trace amounts) was removed from vaccines used in infants starting in the late 1990s, though the preservative-including inactivated influenza vaccine is still available for use in individuals >or=6 months of age. We compared the proportion of injection site reactions, rash, and infections reported to the Vaccine Adverse Event Reporting System (VAERS) after preservative-free (PFV), preservative-including (PIV), and preservative unknown (PUV) vaccines in reports from 7/1/2004 to 1/4/2006. There were 145, 175, and 216 reports after vaccination with PFV, PIV, and PUV, respectively. The most frequently reported coding terms (fever, rash, and urticaria) were seen in similar proportions in the PFV, PIV, and PUV groups. No difference was detected in the proportion of injection site reactions (ISR), rash, or infections in the PIV, PFV, and PUV reports. Keeping in mind the inherent limitations of VAERS, including underreporting and potential reporting biases, we conclude that there were no substantial differences in the proportion of rash, ISR, and infection reports in the PIV, PFV and PUV reports in infants.