Four cases of Saccharomyces boulardii fungemia, a very rare side effect of Saccharomyces boulardii therapy, are reported. The clinical impact of Saccharomyces boulardii infection appeared to be moderate. However, even though organ involvement was never demonstrated, septic shock with no other etiology was observed in one of our patients. All patients had an indwelling vascular catheter. Contamination of the air, environmental surfaces, and hands following the opening of a packet suggests that catheter contamination may have been a source of infection. To prevent catheter contamination it is recommended that packets or capsules of Saccharomyces boulardii be opened with gloves, outside the patient's room.