Anorectal syphilis, one of the great masqueraders in medicine, can be difficult to diagnose not only because of its variable symptoms but also because it is hard to think of unless a detailed history about sexual preferences and practices, including homosexuality, has been gathered. With increasing acceptance of sexual activity in our culture, despite moral and religious issues, various forms of sex have led to many different clinical conditions of sexually transmitted diseases. In this report, we describe a rare case of primary anorectal syphilis with clinical, endoscopic and histologic features that was misdiagnosed as Crohn's disease.