Chronic constipation is one of the most frequent complaints in childhood. Although there is evidence that gastrointestinal flora is important in gut motility, there is little evidence that gut flora is abnormal in constipation. Lactobacilli and bifidobacteria increase stool frequency and decrease consistency in normal individuals. But, according to several reviews, the evidence of probiotics for efficacy in constipation is limited. Fiber supplements, lactose-free diets, and lactobacillus supplementation are effective in the management of children with recurrent abdominal pain and irritable bowel syndrome. Several studies with Lactobacillus GG in children showed negative results in children with chronic constipation. Because Bifidobacterium animalis DN-173 010 has been shown to be effective in adults with constipation-predominant irritable bowel syndrome this study should also be performed in a well-designed large placebo-controlled trial in children with constipation.