We report a case of acute fulminant amoebic colitis that resulted in the development of a perianal ulcer in a 29-year-old Japanese homosexual man with acquired immunodeficiency syndrome (AIDS). The patient was admitted to our hospital with a persistent perianal abscess that was refractory to antibiotic therapy adminis-tered at another hospital. On admission, we observed a giant ulcer in the perianal region. At first, cytomega-lovirus colitis was suspected by blood investigations. Ganciclovir therapy was initiated; however, the patient developed necrosis of the skin around the anus during therapy. We only performed end-sigmoidostomy and necrotomy to avoid excessive surgical invasion. Histopathological examination of the surgical specimen revealed the presence of trophozoite amoebae, indicating a final diagnosis of acute fulminant amoebic colitis. The patient’s postoperative course was favorable, and proctectomy of the residual rectum was performed 11 mo later. Amoebic colitis is one of the most severe complications affecting patients with AIDS. Particularly, acute fulminant amoebic colitis may result in a poor prognosis; therefore, staged surgical therapy as a lessinvasive procedure should be considered as one of the treatment options for these patients. We report a case of acute fulminant amoebic colitis that resulted in the development of a perianal ulcer in a 29-year-old Japanese homosexual man with acquired immunodeficiency syndrome (AIDS). The patient was admitted to our hospital with a persistent perianal abscess that was refractory to antibiotic therapy adminis-tered at another hospital. On admission, we observed a giant ulcer in the perianal region. At first, cytomega-lovirus colitis was suspected by blood investigations. however, the patient developed necrosis of the We only performed endo- sigmoidostomy and necrotomy to avoid excessive surgical invasion. Histopathological examination of the surgical specimen revealed the presence of trophozoite amoebae, indicating a final diagnosis of acute fulminant amoebic colitis. The patient’s postoperative course was favorable , and proctectomy of the residual rectum was performed 11 mo later. Amoebic colitis is one of the most severe complications affecting patients with AIDS. Particularly, acute fulminant amoebic colitis may result in a poor prognosis; therefore, staged surgical therapy as a less invasive procedure should be considered as one of the treatment options for these patients.