Background: In Australia, rates of hepatitis B (HBV) transmission continue to be higher in certain populations, including commercial sex workers and injecting drug users (IDU). This study aims to identify rates and predictors of completion of a HBV vaccination schedule in ?high-risk' attendees of a primary health care centre in Sydney. Methods: All clients who attended Kirketon Road Centre, a primary health care centre located in Kings Cross, Sydney, with no evidence of HBV immunity were included in the cohort. The study design was observational with historical controls. The main outcome measure was completion of a three-dose HBV vaccine schedule in the study period. Results: Among 2085 clients who received a first vaccination, 1013 (49%) received a second and 435 (21%) received a third vaccination. Univariate analysis found that significant predictors of completion of the vaccine schedule were intention to administer an accelerated schedule (OR 1.49, P = 0.004), not being an IDU (OR 1.29, P = 0.02) and shorter time between first visit and first vaccine dose (OR 1.24, P for trend <0.0001); however, on multivariate analysis, not being an IDU was no longer a predictor of vaccine completion. Conclusion: Implementation of an accelerated vaccination schedule improved completion rates but they were still low, despite the provision of free vaccination in a service specifically targeting the needs of sex workers, IDU and other marginalised populations. Increasing HBV vaccine uptake and completion rates in Australian adults is an important public health issue not only for the prevention of HBV but also for the future application of other potential vaccines, including those against HIV and hepatitis C.