A gay man with well-controlled HIV and vaccinated against mpox presented with severe proctitis. Testing revealed anorectal mpox, herpes simplex virus, lymphogranuloma venereum, Neisseria gonorrhoeae and Mycoplasma genitalium. Serology was indicative of infectious syphilis. This case highlights the need to consider a wide range of concurrent sexually transmitted infections in patients with proctitis, including those vaccinated against mpox.