The authors present the case of a 32-year-old Caucasian male, engineer, who was submitted to a colonoscopy after a presumptive diagnosis of ulcerative colitis. The patient referred an acute bloody and mucous diarrhea, lasting for three weeks, with no fever or rectal tenesmus. Stool studies were negative. During the procedure, colonic segments with continuous hyperemic and exudative mucosa, with small papules with apical ulcers and erosions, were observed.