A 32-year-old man is evaluated in a sexual health clinic with a 4-day history of painless penile lesions (Figure 1). His sex partners are men, and he has had 2 partners in the last 6 months. Physical examination reveals three nontender ulcers on the lateral aspect of the penile shaft and firm, nontender lymphadenopathy in the right inguinal region. Oral examination and skin inspection are normal. He has no neurologic symptoms. A clinical diagnosis of syphilis is strongly suspected; nontreponemal and treponemal serologic tests for syphilis are ordered.