Background. There are few data on overweight in children in developing countries. Such data are important to guide public health policy. We assessed trends in the prevalence of overweight and obesity in children from the Seychelles, a middle-income island state in the Indian Ocean. Methods. Multiple cross-sectional surveys were conducted each year between 1998 and 2004 on all students of all schools in four selected school grades (crèche, 4th, 7th and 10th years of mandatory school). Weight and height were measured and children were asked about walking time and frequency of physical exercise at leisure time. Excess weight categories were defined according to the criteria of the International Obesity Task Force (IOTF) and the U.S. Centers for Disease Control and Prevention (CDC). Results. Data were available for 33?340 observations in 1998-2004, corresponding to 23?459 individual children measured once or several times. Based on IOTF criteria, the prevalence of 'overweight' or 'obesity' increased from 8.7% to 13.5% in boys, and from 11.8% to 18.6% in girls from 1998 to 2004 (P<0.001). The prevalence of 'obesity' increased from 2.1% to 5.2% in boys and from 3.1% to 6.2% in girls (P<0.001). Using CDC criteria, the prevalence of 'at risk of overweight' and 'overweight' increased by similar proportions. The shift towards higher values over time was larger in the upper than the lower tail of the BMI distribution. Physical activity decreased over calendar years and was inversely associated with excess weight. Conclusions. The prevalence of excess weight increased markedly over a seven-year period in children in the Seychelles. This is likely to reflect a rapid nutrition transition with increasingly positive energy balance. These findings stress the need for programs and policies aimed at promoting physical activity and healthy nutrition in countries in epidemiological transition. [Authors]