Escherichia coli O157: H7 became an important pathogen starting in the early 1980s. It has caused epidemics and sporadic cases of often bloody diarrhea which may progress to severe hemolytic and uremic syndrome or thrombotic thrombocytopenia purpura. E. coli O157: H7 is mainly transmitted in food, water and interhuman transmission, but direct animal-to-man transmission has also been documented. E. coli O157: H7 can adhere tightly to the enterocyte brush border (eae gene) and produce verotoxins or Shiga-like toxins and hemolysine (ehxA gene). Diagnosis of E. coli O157: H7 infections is based on evidencing the germ in stools and/or by identifying the genes coding for verotoxins or by serology which increased serum titre of specific antilipopolysaccharide antibodies. Antidiarrheal drugs and antibiotics have little place in the treatment of bloody diarrhea. This public health problem, requires careful identification of animal reservoirs and improved population education in food hygiene.