Syphilis is a sexually transmitted disease which is still common. Traditionally, serology has been the diagnostic gold standard. The pathology of the lesions, especially those of secondary syphilis, can vary. Spirochetes (Treponema pallidum) can be detected with silver staining, but with only low sensitivity. Since the 1990s, immunohistochemistry against Treponema has been available. The pathology and immunohistochemistry of 42 biopsies from patients with a possible clinical diagnosis of syphilis were examined. In secondary syphilis, treponemas were detected in 83.3%of the cases using immunohistochemistry.