Introduction: Constipation is a common complaint in children and early intervention with oral laxatives may improve complete resolution of functional constipation. However, most treatment guidelines are based on reviews of the literature that do not incorporate a quality assessment of the studies. Objective: To investigate and summarise the quantity and quality of the current evidence for the effect of laxatives and dietary measures on functional childhood constipation. Methods: The Medline and Embase databases were searched to identify studies evaluating the effect of a medicamentous treatment or dietary intervention on functional constipation. Methodological quality was assessed using a validated list of criteria. Data were statistically pooled, and in case of clinical heterogeneity results were summarised according to a best evidence synthesis. Results: Of the 736 studies found, 28 met the inclusion criteria. In total 10 studies were of high quality. The included studies were clinically and statistically heterogeneous in design. Most laxatives were not compared to placebo. Compared to all other laxatives, polyethylene glycol (PEG) achieved more treatment success (pooled relative risk (RR): 1.47; 95% CI 1.23 to 1.76). Lactulose was less than or equally effective in increasing the defecation frequency compared to all other laxatives investigated. There was no difference in effect on defecation frequency between fibre and placebo (weighted standardised mean difference 0.35 bowel movements per week in favour of fibre, 95% CI -0.04 to 0.74). Conclusion: Insufficient evidence exists supporting that laxative treatment is better than placebo in children with constipation. Compared to all other laxatives, PEG achieved more treatment success, but results on defecation frequency were conflicting. Based on the results of this review, we can give no recommendations to support one laxative over the other for childhood constipation.