RATIONALE: Several studies have reported that both short and long sleep durations are associated with the metabolic syndrome (MetS), but whether a dose-response relationship exists is unclear. OBJECTIVE: We performed a meta-analysis to study the magnitude of the association between the different durations of sleep and MetS. METHODS: We searched in the databases of PubMed, Web of Science and Ovid (All Journals@Ovid) from inception to October 4th, 2014 for cross-sectional studies where an association between MetS and sleep duration was analyzed. MEASUREMENTS AND MAIN RESULTS: 18 studies with 75,657 participants were included. Daily sleep duration of 7 to 8 hours was used as the reference group. The odds ratio (OR) of having MetS for short (<7 hours) sleep was 1.23 ([95% CI: 1.11 to 1.37], p < 0.001, I2 71%). The ORs for <5 hours, 5 to 6 hours, and 6 to 7 hours of sleep were: 1.51 ([95% CIs: 1.10 to 2.08], p = 0.01); 1.28 ([95% CIs: 1.11 to 1.48], p < 0.001); and 1.16 ([95% CI: 1.02 to 1.31], p = 0.02), respectively. The coefficient of sleep duration on log of ORs was -0.06 + 0.02 (p = 0.02). The OR for long sleep duration was 1.13 ([95% CI: 0.97 to 1.32], p = 0.10, I2 89%). CONCLUSIONS: A dose-response relationship exists between short sleep duration and MetS. Those who report a sleep duration of <5 hours have a 1.5 higher odds of having MetS. Our study does not support the notion that long sleep is associated with MetS