Consumption of dark chocolate, a rich source of flavonoids, has been associated with reduced risk of cardiovascular disease. However, underlying pathophysiologic mechanisms are not fully elucidated. We reviewed existing evidence on the effect of cocoa consumption on flow-mediated dilation (FMD) by conducting a literature search using PubMed and Embase for completed, randomized, controlled trials. The primary effect measure was the difference in means of the final measurement between the intervention and control groups. Nineteen clinical trials with a total of 454 participants were included. Treatment duration ranged from 2 hours to 12 weeks. Pooled estimate showed that intervention with dark chocolate significantly increased FMD levels by 2 % (95 % confidence interval 1.6-2.39 %) compared with placebo/control group. Similar results were seen when stratified by study design, geographic location, cocoa dose, or study quality. In addition, the effect size was greater in individuals with cardiovascular risk factors. In summary, intervention with cocoa improved endothelial function as measured by FMD.