BACKGROUND The aim of the study was to assess the microbiological characteristics and the clinical aspects of pediatric patients (age < 14 years) with infectious diarrhea due to one of the species included among the mesophilic Aeromonas group (AMs) from January 1989 to December 1991. METHODS The samples (stools) were processed following the routine methodology recommended. For isolation of AMs the XDCA medium was used and identification of species was performed by gas production tests from glucose and esculin hydrolysis. Clinical and epidemiologic features were recorded by means of a retrospective analysis of the clinical histories. RESULTS In 30.3% of the 7,653 stool-cultures studied, an enteropathogenic microorganism identified as S. enterica (I) was isolated in 979 (12.8%), 536 cases to Campylobacter sp. (7.0%) infection, 58 to Shigella sp. (0.7%), 56 to Y. enterocolitica (0.7%, 221 to rotavirus (2.8%) and 49 to adenovirus (0.6%) The presence of AMs was detected in 282 patients (3.7%), representing 12% of the all positive stool-cultures. The species isolated were A. caviae (54.9%), A. sobria (21.9%) and A. hydrophila (23.1%). In 56% of the cases the AMs were isolated as the single pathogen. Thirty-nine point seven percent of the isolations were performed in patients aged less than 12 months (17% with less than 3 months). The A. caviae species was found to be predominant among the breast-fed babies (51.7%). Seventy percent of the children of 0-3 months presented A. caviae as unique pathogen. A total of 84.3% of the children infected with A. caviae, had been or were being fed with artificial lactation. AMs predominated in the late summer-early fall months (August-October) reading the maximum rate of isolations in these months (35.3 cases/month). CONCLUSIONS Infections gastroenteritis due to mesophilic Aeromonas in the authors' geographic area appears to affect males mainly, and presents as an acute self-limited diarrhea, community-acquired. The predominance of A. caviae during the lactation period and in the first three months of life are data which should be further considered and confirmed.