Background: Probiotics are increasingly used in the treatment of functional gastrointestinal disorders. Studies in constipated adults with a Bifidus yoghurt (containing Bifidobacterium breve, Bifidobacterium bifidum and Lactobacillus acidophilus) showed a significant increase in defecation frequency. The aim of this pilot study was to determine if Bifidobacterium breve is effective in the treatment of childhood constipation. Methods. Children, 3 to 16 years of age, with functional constipation according to the Rome III criteria were eligible for this study. During 4 weeks, children received one sachet of powder daily, containing 108- 1010 CFU Bifidobacterium breve. Furthermore, children were instructed to try to defecate on the toilet for 5-10 minutes after each meal and to complete a standardized bowel diary daily. The primary outcome measure was change in defecation frequency. Secondary outcome measures were stool consistency using the Bristol stool scale frequency of episodes of faecal incontinence, pain during defecation, frequency of abdominal pain, frequency of adverse effects (nausea, diarrhoea and bad taste), and frequency of intake of bisacodyl. Results: Twenty children (75% male, mean age 7.4) were included in this pilot study. The defecation frequency per week significantly increased from 0.9 (0-2) at baseline to 4.9 (0-21) in week 4 (p < 0.01). The mean stool consistency score increased from 2.6 (2-4) at baseline to 3.5 (1-6) in week 4 (p = 0.03). The number of faecal incontinence episodes per week significantly decreased from 9.0 (0-35) at baseline to 1.5 (0-7) in week 4 (p < 0.01). Abdominal pain episodes per week significantly decreased from 4.2 (0-7) at baseline to 1.9 (0-7) in week 4 (p = 0.01). No side effects occurred. Conclusion: Bifidobacterium breve is effective in increasing stool frequency in children with functional constipation. Furthermore it has a positive effect with respect to stool consistency, decreasing the number of faecal incontinence episodes and in diminishing abdominal pain. A randomized placebo controlled trial is required to confirm these data. © 2011 Tabbers et al; licensee BioMed Central Ltd.