Acute gastroenteritis (AGE) in children is still one of the most important causes of mortality and morbidity in developing countries. Therefore, it is very important for clinicians to detect the presence and severity of acute gastroenteritis. Red cell distribution width (RDW) is thought to have the potential for AGE evaluation in children. We sought to investigate the value of RDW for severity assessment in children with AGE. A total of 97 AGE patients were included in a prospective observational study. Complete blood count, serum C-reactive protein, and stool examinations were carried out. Modified Vesikari score (MVS) was evaluated to determine severity. Median age was 19months (min-max, 1-198months). The male/female ratio was 1.55 (59/38). Rotavirus was detected in 31 of 97 children (32%). median MVS was 9 points (min-max, 5-24 points). A total of 32 (33%), 43 (44%) and 22 patients (23%) were classified in the mild-, moderate-, and high-severity groups, respectively. There were no significant differences between rotavirus-positive and rotavirus-negative children. Hemoglobin, mean corpuscular volume, and RDW differed significantly according to severity. RDW had the highest area under the curve when the high-severity group was compared with the combination of low- and moderate-severity groups on receiver operating characteristic analysis. Red cell distribution width increased with the increase in severity of AGE. RDW may offer additional severity stratification in children with AGE.