Enteropathogenic Escherichia coli is the most important cause of acute diarrhea in developing countries, specially in infants under one year of age. Enteropathogenic Escherichia coli strains are able to induce profound cytoskeletal alterations in the enterocyte known as attaching and effacing lesions, associated with the formation of cuplike pedestals. We report an Enteropathogenic Escherichia coli O11ab:H2 strain isolated from an infant with acute diarrhea, on the eleventh day of disease, that caused attaching and effacing lesion and penetrated the enterocyte, as well as invaded the HeLa cell tissue culture in vitro and the rabbit ileal loop assay in vivo, in the ultrastructural study. This observation indicates that the severe lesions of the small bowel caused by an enteropathogenic Escherichia coli O111ab:H2 strain can occur even in the early stages of the infection.