Sexually transmitted diseases of the colon, rectum, and anus. The challenge of the nineties. During the past two decades, an explosive growth in both the prevalence and types of sexually transmitted diseases has occurred. Up to 55 percent of homosexual men with anorectal complaints have gonorrhea; 80 percent of the patients with syphilis are homosexuals. Chlamydia is found in 15 percent of asymptomatic homosexual men, and up to one third of homosexuals have active anorectal herpes simplex virus. In addition, a host of parasites, bacterial, viral, and protozoan are all rampant in the homosexual population. Furthermore, the global epidemic of AIDS has produced a plethora of colorectal manifestations. Acute cytomegalovirus ileocolitis is the most common indication for emergency abdominal surgery in the homosexual AIDS population. Along with cryptosporidia and isospora, the patient may present to the colorectal surgeon with bloody diarrhea and weight loss before the diagnosis of human immunodeficiency virus (HIV) disease. Other patients may present with colorectal Kaposi's sarcoma or anorectal lymphoma, and consequently will be found to have seropositivity for HIV. However, in addition to these protean manifestations, one third of patients with AIDS consult the colorectal surgeon with either condylomata acuminata, anorectal sepsis, or proctitis before the diagnosis of HIV disease. Although aggressive anorectal surgery is associated with reasonable surgical results in some asymptomatic HIV positive patients, the same procedures in AIDS (symptomatic HIV positive) patients will often be met with disastrous results. It is incumbent upon the surgeon, therefore, to recognize the manifestations of HIV disease and diagnose these conditions accordingly. 