Aim:Non-invasive body contouring is a promising modality. However, due to a lack of good evidence-based data, the mechanism by which contouring occurs remains unclear. The purpose of this study was to evaluate the effect of treatment with the Contour I? ultrasound system (Ultrashape?, Syneron?, Israel) on abdominal circumference and to compare 2 power levels for efifcacy and safety. Methods:A prospective, self-controlled double-blind design was used. Thirty-six women, aged 30-45 years, were randomized to receive treatment with the Contour I at high or low acoustic outputs in 3 successive sessions, 1 month apart. Safety was evaluated by adverse events, local skin reaction, and pain. Efifcacy was evaluated by the change in abdominal circumference relative to baseline and to the untreated thigh area (intal control). Patients were followed for 28 days after the last treatment session. Results:At 1 month after the ifrst session, the mean reductions in abdominal circumference measured 1.65 cm (P<0.001) and 0.87 cm (P<0.019) in the high and low-power groups, respectively. At 1 month after the last session, the cumulative reductions in circumference were 2.56 cm (P<0.001) and 1.49 cm (P<0.012), respectively. There was no change in the intal-control circumference throughout treatment. There were no treatment-induced severe adverse events. Conclusion: Multiple successive treatments of the abdominal area with the Contour I lead to a signiifcant progressive reduction in circumference. The magnitude of the reduction is directly correlated to the acoustic power output which suggests that the technology itself is the main cause for the contouring effect.