AIM: Melatonin seems to have a positive impact on the brain-gut axis and many direct and indirect effects on the gastrointestinal tract. This trial aimed at assessing the efficacy of melatonin combined with Lactobacillus Rhamnosus GG given in the treatment of paediatric patients with functional abdominal pain disorders. METHODS: Forty-two patients aged 4-18 years old who fulfilled the Rome IV Diagnostic Criteria for functional abdominal pain disorders were enrolled. Melatonin 3 or 5 mg in combination with Lactobacillus Rhamnosus GG (group 1, n = 22) or a placebo in combination with Lactobacillus Rhamnosus GG (control group, n = 20) were taken in the evening for a period of 4 weeks. The study duration was 12 weeks. The primary study endpoint was represented by clinical improvement at week 12 - defined as at least a 50% reduction in mean abdominal pain index (API) from baseline to week 12. RESULTS: The mean API was reduced by more than 50% between T0 and T2 in the group of children treated with melatonin. However, the difference in the distributions of the variations of the scores between the two groups was not significant between T0 and T2 (P = 0.082), while it was significant between T0 and T1 (P = 0.001). Similar results were obtained by analysing the API variables 'weekly frequency of pain' (item 1) and 'perceived intensity of pain' (item 4) individually. CONCLUSIONS: This is the first study to investigate the role of the combination of melatonin and Lactobacillus Rhamnosus GG in the treatment of children with functional abdominal pain disorders. Melatonin combined with Lactobacillus Rhamnosus GG can be considered a therapeutic option for these conditions in children.