The Treponema pallidum subspecies pallidum is the etiologic agent of syphilis. Syphilis is usually transmitted sexually, but it can also be passed vertically from mother to child either in utero (congenital syphilis) or perinatally during birth. Regardless of the mode of transmission, untreated cases of syphilis can result in multisystem involvement with significant morbidity. The disease is systemic and is characterized by periods of latency. Serologic testing is the preferred method of diagnosis. Two types of serologic tests are used: treponemal and nontreponemal assays. Traditional serologic screening for syphilis begins with a nontreponemal test followed by a treponemal test to confirm reactive results. Reverse screening algorithms begin with a treponemal test followed by a nontreponemal test to confirm reactive results.