Previous experience in our hospital and in the literature indicate an incidence of diarrhea between 5% and 50% after antibiotic treatment (depending on the antibiotic used). In the present study, a total of 199 patients receiving antibiotic treatment after surgical intervention received additionally to their antibiotic treatment daily two sachets of the multispecies probiotic MSP. The application of MSP reduced the incidence of diarrhea to 0.5% (1 patient out of the199 probands). The probiotic administration was forgotten in two subjects, both generated AAD (with evidence of Clostridium difficile in one subject). In conclusion, the use of the multispecies probiotic for primary prevention of AAD was found to be successful. Prevention of AAD in this manner promises to result in a reduction of overall costs for health care.