A 23-year-old man presents for evaluation of a new nontender penile lesion that has slowly developed over several weeks. He has insertive and receptive anal sex with male partners and inconsistently uses condoms. He denies other symptoms, has no chronic medical problems, and has no antibiotic allergies. Physical examination reveals a 1 cm, nontender ulcer on the dorsal surface of his penis (Figure 1) and no other significant findings. Laboratory studies reveal a positive syphilis enzyme immunoassay (EIA) and a positive Rapid Plasma Reagin (RPR) at a titer of 1:32. He has never been diagnosed with or treated for syphilis in the past. An HIV-1/2 antigen-antibody test is negative.