We report four cases of primary syphilis of the penis in HIV-negative men having unprotected insertive oral sexual intercourse with men. Patients presented with atypical penile lesions mimicking genital herpes, balanitis, lichen planus and fi xed drug eruption. Syphilis should be considered in the differential diagnosis of other genital diseases, both sexually or non-sexually transmitted. Considering the increasing incidence of atypical manifestations of syphilis, serological tests for syphilis should also be performed more often.
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