Central line-associated bloodstream infection (CLABSI) rates are an important measure of health care quality. However, reputational or financial risks associated with public reporting and disclosure of hospital CLABSI rates may introduce reporting biases, including intentional underreporting. To assess systematic case misclassification of CLABSI to secondary bloodstream infection (BSI; ie, intentional underreporting of CLABSI), the authors assessed data reported to the National Healthcare Safety Network by hospitals in Pennsylvania, the only state in which both CLABSI and secondary BSI reporting are mandatory. CLABSI rates decreased over the 2-year analysis period, but the authors found no evidence of increasing secondary BSI rates, suggesting that systematic case misclassification is not widespread.