Background:Little information is available on the epidemiologic characteristics of antibiotic‐associated diarrhea (AAD) in children. The authors' aim was to evaluate the incidence of AAD in an outpatient pediatric population and to identify risk factors.Methods:Children aged 1 month to 15.4 years treated with oral antibiotics for a proven or suspected infection were enrolled from an ambulatory pediatric practice during an 11‐month period. Parents recorded the daily frequency and characteristics of stools using a diary during the antibiotic treatment and for 1 week after it was stopped. An episode of diarrhea was defined by at least 3 soft or liquid stools/d for at least 2 consecutive days. Risk factors for AAD—age, type of antibiotic treatment, type of combined treatment, and site of infection— were analyzed.Results:Of 650 children included, 11% had an episode of AAD, lasting a mean of 4.0 ± 3.0 days, beginning a mean of 5.3 ± 3.5 days after the start of antibiotic treatment. No child was hospitalized because of AAD. The incidence of AAD was higher in children less than 2 years (18%) than in those more than 2 years (3%;P< 0.0001). The incidence of AAD was particularly high after administration of certain antibiotics (amoxicillin/clavulanate, 23%;P= 0.003 compared with other antibiotics). The type of combined treatment and site of infection did not influence the onset of AAD.Conclusions:Antibiotic‐associated diarrhea was common in these outpatient children, especially for those aged less than 2 years and after the prescription of certain antibiotics, particularly, the combination of amoxicillin/clavulanate.JPGN 37:22‐26, 2003.