the first case concerns a 73-year-old male patient with clinical history of cardiovascular disease and pulmonary insufficiency, admitted to the hospital for urinary tract infection and was treated with broad-spectrum antibiotics for a long period of time. During his hospitalization he developed abdominal pain and haematochezia. The second case concerns a 64-year-old woman treated with antibiotics for community-acquired pneumonia. After the treatment she developed abdominal pain and diarrhea. In both cases the colonic biopsy showed pseudomembranous colitis with presence of signet-ring cells within dilated crypts of the colonic mucosa. The presence of signet-ring cells is a rare finding in pseudomembranous colitis and may lead to misdiagnosis of signet-ring carcinoma of the colon.