We evaluated sensitivity, specificity, and predictive values of the ICD-9 coding system for surveillance of chronic hepatitis B virus infection (HBV) using data from an observational cohort study. All HBV cases were validated by chart review. Of 1,652,055 adult patients, 2,202 (0.1%) were included in the cohort based upon laboratory data or hepatitis B ICD-9 codes. Use of one ICD-9 code had a sensitivity of 83.9%, positive predictive value of 61.0%, and specificity and negative predictive values > 99%. Our findings suggest that use of one or two hepatitis B ICD 9 codes can identify cases with chronic HBV infection.