Diagnosis and treatment of syphilis are challenging because of its variable clinical presentation and course and the lack of definitive tests of cure after treatment. This review of the most recent literature on the epidemiology, clinical manifestations, current diagnosis, and treatment of syphilis is focused toward clinicians who treat patients with this disease. Syphilis coinfection with human immunodeficiency virus is emphasized because it is increasingly common in the United States and affects the initial presentation, disease course, diagnosis, and treatment of syphilis. Of particular consequence is the effect of human immunodeficiency virus on the clinical diagnosis, prevalence, and course of neurosyphilis, one of the most serious consequences of syphilis infection. linicians from large metropolitan areas frequently face the challenge of diagnosing syphilis and treating patients with syphilis. In doing so, they are often faced with questions regarding interpretation of clinical findings and laboratory results and selection of appropriate therapy. Interpretation of the data available to answer these questions is often challenging given the paucity of large well-designed studies and the substantial variability that characterizes the clinical presentation of syphilis. Such a challenge is particularly found in the treatment of patients coinfected with syphilis and human immunodeficiency virus (HIV). To guide clinicians in this difficult task, we discuss the most recent literature on the epidemiology, clinical manifestations, diagnosis, and treatment of syphilis and the corresponding effects of HIV coinfection.