We looked for C. difficile and its cytotoxin among children and adolescents treated with diverse kinds of cancer chemotherapy in an oncologic ward of a pediatric hospital. Most of them were also given multiple antibiotic treatments, susceptible of making C. difficile colonization easier due to the modification of the intestinal ecosystem. As the colonization may have an external origin, we also looked for C. difficile in the environment. 14 patients have been studied and we found cytotoxic strains in four of them and non cytotoxic ones in two. This paper discusses the influence of cancer chemotherapy and antibiotherapy on C. difficile colonization among those patients, and the role played by this bacteria and its toxin on the diarrhea cycle. The facts that several patients have been colonized together and that environmental samples showed up positive, lead us to suspect a nosocomial spread. To confirm this thesis, strains originating from patients and environments were compared.