The hepatitis B virus is hyperendemic in Hong Kong. Health care workers are at increased risk of acquiring hepatitis B because of frequent exposure and are therefore advised to receive hepatitis B vaccination. Immune response rates among 1102 female and 567 male health care workers in Hong Kongwere examined and analysed. There was a good overall response rate of 93.8%, with women responding better than men. Among female health care workers, the proportion with an inadequate antibody response increased from 3.5% in those younger than 35 years old to 6.5% in those aged 35 years and older. Post-vaccination testing should be recommended to identify non-responders and to guide post-exposure management.