Evidence from the literature has shown that Saccharomyces boulardii provides a clinically significant benefit in the treatment of acute infectious diarrhoea in children. In this multicentre, randomised, prospective, controlled, single blind clinical trial performed in children with acute watery diarrhoea, we aimed to evaluate the impact of S. boulardii CNCM I-745 in hospitalised children, in children requiring emergency care unit (ECU) stay and in outpatient settings. The primary endpoint was the duration of diarrhoea (in hours). Secondary outcome measures were duration of hospitalisation and diarrhoea at the 3rd day of intervention. In the whole study group (363 children), the duration of diarrhoea was approximately 24 h shorter in the S. boulardii group (75.4 +/- 33.1 vs 99.8 +/- 32.5 h, P<0.001). The effect of S. boulardii (diarrhoea-free children) was observed starting at 48 h. After 72 h, only 27.3% of the children receiving probiotic still had watery diarrhoea, in contrast to 48.5% in the control group (P<0.001). The duration of diarrhoea was significantly reduced in the probiotic group in hospital, ECU and outpatient settings (P<0.001, P<0.01 and P<0.001, respectively). The percentage of diarrhoea-free children was significantly larger after 48 and 72 h in all settings. The mean length of hospital stay was shorter with more than 36 h difference in the S. boulardii group (4.60 +/- 1.72 vs 6.12 +/- 1.71 days, P<0.001). The mean length of ECU stay was shorter with more than 19 h difference in the probiotic group (1.20 +/- 0.4 vs 2.0 +/- 0.3 days, P<0.001). No adverse effects related to the probiotic were noted. Because treatment can shorten the duration of diarrhoea and reduce the length of ECU and hospital stay, there is likely a social and economic benefit of S. boulardii CNCM I-745 in adjunction to oral rehydration solution in acute infectious gastroenteritis in children.