Acquisition of HSV, N. gonorrhoeae, or C. trachomatis (including lymphogranuloma venereum [LGV] strains of C. trachomatis) during receptive anorectal intercourse causes most cases of infectious proctitis in women and in men who have sex with men (MSM). Sexually acquired proctocolitis is most often due to Campylobacter or Shigella spp. In MSM without HIV infection, enteritis is often attributable to Giardia lamblia.