Stool samples from children and adults with and without diarrhea were examined for the presence of enterotoxigenic Bacteroides fragilis (ETBF) and its enterotoxin. A cytotoxic assay with HT-29 cells followed by neutralization with a hyperimmune antiserum were used to detect B. fragilis enterotoxin. ETBF isolates were recovered from 12% of healthy children and 17% of children with diarrhea (P = .42) and from 15% of healthy adults and 9.4% of adults with diarrhea (P = .31). Fecal B. fragilis enterotoxin was detected in four children (two with diarrhea and two without diarrhea) and in four adults with diarrhea. This study shows that in Italy, the rate of ETBF carriage is high, regardless if diarrhea is present. In some instances, the presence of ETBF is associated with detectable levels of fecal enterotoxin, but the significance of this finding deserves further evaluation.