Malignant syphilis is a rare and severe variant of secondary syphilis. It is clinically characterized by large papular, nodular and ulcerative lesions affecting the trunk and the extremities and covered with thick crust. We present a case of 52-year-old homosexual male who developed malignant syphilis and this was the first clinical manifestation of HIV infection. The patient was treated successfully with intravenous aqueous crystalline penicillin G. Physicians should recognize malignant syphilis and consider it in all HIV-infected individuals with ulceronodular skin lesions.