Gastrointestinal involvement is a rare event in patients with B-cell chronic lymphocytic leukemia (B-CLL) and is usually associated to lymphomatous transformation. However, in autopsy studies the reported incidence of microscopic infiltration can reach up to 50% of cases. Seven B-CLL patients in advanced stage/progressive disease were evaluated by colonoscopy because of continuous diarrhea. Five out of seven patients (71%) presented histological evidence of colonic infiltration. Persistent diarrhea in patients with progressive/advanced B-CLL can be a clinical sign of intestinal infiltration and justifies endoscopic examinations.