The design of this study is a cluster-randomized controlled trial with stepped wedge design that will gradually introduce the intervention across clinics. This pragmatic approach incorporates a concurrent comparison group, allows for assessment of time trends, will be well-powered, and will generate more generalizable results due to its inclusion of multiple clinics. The intervention will be operationalized as standing orders for syphilis serology when there is an order for HIV viral load and/or CD4 cell count. Data sources include (1) syphilis tests submitted to the Public Health Ontario Laboratory; (2) a standardized clinical worksheet and medical chart review to validate diagnoses for screen test positives; and (3) data collected from a subset of patients via their participation in the ongoing Ontario HIV Treatment Network (OHTN) Cohort Study. The latter follows adults in HIV care and collects data using chart reviews and annual face-to-face interviews including measures of sexual behaviour.