A man in his 20s with male and female sexual partners presented with month-long progressive, painful, annular, and scalloped erosions on the glans. He denied urethral discharge or other systemic symptoms. Physical examination revealed edema and oozing erosions on the glans and coronal sulcus (Figure). No enlarged lymph nodes or other cutaneous lesions were present. Screening tests for sexually transmitted infections (STIs) were performed, including herpes simplex virus (HSV) polymerase chain reaction (PCR), bacterial and fungal cultures of swabs from erosive lesions, and serologic tests for HIV and syphilis; all results were negative. Under the initial clinical suspicion of HSV infection, he was unsuccessfully treated with valaciclovir. However, a PCR study of a swab sample was positive for Treponema pallidum. A diagnosis of syphilitic balanitis of Follmann (SBF) was made, and the patient was successfully treated with a single intramuscular dose of benzathine penicillin G, 2.4 mIU.