Objective To determine whether administration of Lactobacillus reuteri DSM 17938 is beneficial in functional abdominal pain (FAP) of childhood. Study design A total of 101 children, aged 6-15 years, who fulfilled the Rome III criteria for FAP were enrolled in a randomized double-blind, placebo-controlled trial, and were randomly assigned to receive either L reuteri DSM 17938 or placebo for 4 weeks, with further follow-up of additional 4 weeks. Response to therapy was based on a self-reported daily questionnaire monitoring frequency and intensity of abdominal pain, using the faces scoring system by Hicks. Results L reuteri (n = 47) was significantly superior to placebo (n = 46) in relieving frequency (1.9 ± 0.8 vs 3.6 ± 1.7 episodes/wk, P <.02) and intensity (4.3 ± 2.2 vs 7.2 ± 3.1 Hicks score/wk, P <.01) of abdominal pain following 4 weeks of supplementation. There was no difference in school absenteeism rate or other gastrointestinal symptoMS except for a lower incidence of perceived abdominal distention and bloating, favoring L reuteri. Conclusions L reuteri DSM 17938, compared with placebo, significantly reduced the frequency and intensity of FAP in children.