Objective: There are limited controlled data for intragastric balloons (IGB) in obesity treatment. This randomized, controlled study evaluated the efficacy and safety of an IGB in obese individuals with metabolic syndrome (MS). Design and Methods: Sixty-six adults (BMI: 30-40 kg/m 2 ) were randomized to IGB for 6 months, with a 12 month behavioral modification (IGB Group; ''IGBG''), or 12 month behavioral modification alone (Control Group; ''CG''). The primary outcome was percentage change in body weight. Results: Thirty-one subjects (female: 68%; mean age: 43; mean BMI: 36.0) were randomized to IGBG and 35 (66%; 48; 36.7) to CG. At 6 months, there was a significantly greater weight loss in the IGBG: À14.2 vs. À4.8; P < 0.0001. This was associated with a significantly greater reduction in waist circumference, and an improvement in quality of life, with a trend for a larger %MS remission (50% vs. 30%; n.s.). At month 12, the differences in weight loss were enduring: À9.2 vs. À5.2; P ¼ 0.007. Gastrointestinal-related adverse events were common in the IGBG, resolving predominantly within two weeks. The IGB was removed prematurely in three subjects (one for refractory gastrointestinal symptoms). Conclusions: Statistically significant and clinically relevant improvements in weight loss and health outcomes were observed with the IGBG at 6 months versus behavioral modification alone. The differential weight loss was still evident 6 months after IGB removal.