Aeromonas species were isolated from 0.61% of 34,311 fecal samples during a 5-year period. Most strains belonged to DNA hybridization groups (HG) 4 (A. caviae), 8 (A. sobria), and 1 (A. hydrophila). Mannitol-negative A. schubertii (HG 12) and ornithine-positive A. veronii (HG 10) were not found. Multivariate analysis of the clinical data showed that Aeromonas-associated diarrhea cannot be attributed solely to cytotoxin production of the strains, but that it is also strongly associated with host factors.