It is strange that almost 100 years since the death of Sir William Osler, syphilis has re-emerged as a major public health problem in the developed world. This is despite the enormous medical advances made over the last 50 years. In addition, the overall public health burden of sexually transmitted infections (STIs) has also, paradoxically, increased over the last 30 years. Most humans are sexually active at some point in their adolescent and adult lives and therefore at risk of acquiring and transmitting an STI. In most branches of medicine, one or more STIs may be part of the differential diagnosis. This chapter will outline the current epidemiological picture, consider sexual behaviours and the assessment of patients at risk of STIs, and review the diagnosis and management of infections that are particularly relevant to the practise of coloproctology.