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.A rare subtype of primary syphilis, SBF accounts for less than 0.5% of cases, 1 and is characterized by exudative, welldemarcated, scattered erosions of the glans and prepuce with or without edema. 2 Some cases have also been described with just dry, dark red induration and desquamative balanitis. 3 A typical primary chancre may precede, accompany, or follow the occurrence of SBF. Concomitantly, lymph nodes may or may not be enlarged, depending on the phase of the disease. 2,4 The diagnostic challenge of SBF, even for experienced dermatologists, is owing to its clinical resemblance to genital herpes or Candida infection, and thus it may be underdiagnosed. Diagnosis is usually made with visualization of spirochetes under dark-field microscopy or following a positive lesional PCR swab finding. Serologic studies may be negative early in the disease, especially when palpable lymph nodes are not detected. 2 When negative, serologic studies should be repeated if there is high clinical suspicion. 2 On the other hand, other pathogens such as Candida, HSV, streptococci, and anaerobes must be ruled out. 2,4 Treatment of SBF requires intramuscular administration of 1 dose of benzathine penicillin G, 2.4 mIU. [1][2][3][4] If left untreated, cutaneous lesions will heal spontaneously, but the disease will progress to secondary, latent, and/or tertiary syphilis; therefore, a high clinical suspicion and early administration of adequate treatment are mandatory. 2