In 2008, the PHSKC system (which searches through admission and discharge diagnoses) identified 180 patients hospitalized with influenza, compared with 161 patients identified by CHARS (which is based on discharge diagnoses exclusively). Thus far, PHSKC has reviewed 46 charts from 8 hospitals to validate system accuracy; review of data from the remaining hospital is pending. We identified 3 hospitals that were transmitting incorrect data to PHSKC and requested correction and resubmission of historical data from these hospitals. Preliminary analysis revealed that 35 of the 180 influenza hospitalizations captured by the PHSKC system (19%) were missed by CHARS; however, 15 of these patients (43%) were admitted with presumptive diagnoses of influenza but were determined not to have influenza by the time of discharge. Also, 28 of 161 influenza hospitalizations (17%) captured by CHARS were missed by the PHSKC system; however, we had no means of reverse-identifying CHARS records and, therefore, could not evaluate the validity of these data by chart review.