OBJECTIVES: To establish the prevalence of overweight and obesity and related risk factors in children from Seychelles (Indian Ocean), a country in rapid economic and epidemiological transition. DESIGN: Cross-sectional study with retrospective access to early life data. SUBJECTS: All children from all schools of Seychelles, in four selected school grades (kindergarten, fourth, seventh and tenth year of obligatory school) in 1999. A total of 5514 children aged 4.5-17.4 y were measured, corresponding to 83.5% of the eligible population. MEASUREMENTS: Overweight and obesity, using age- and sex-specific body mass index (BMI) cut-off points as defined by the International Obesity Task Force. RESULTS: Some 12.6% (95% confidence interval: 11.8-13.5%) of the children were overweight and 3.8% (3.3-4.4%) were obese. Weight gain (kg) during the first year of life was strongly associated with subsequent overweight (odds ratio 1.46, 95% confidence interval 1.27-1.67) and obesity (1.59, 1.29-1.97) in childhood, independently of birth weight. Increased maternal BMI (kg/m(2)) was also associated with overweight (1.07, 1.03-1.10) and obesity (1.09, 1.04-1.14) in the offspring. CONCLUSION: Prevalence of overweight and obesity among school children in Seychelles was as high as or higher than in some industrialized countries. If confirmed in other environments, the strong association between weight gain during the first year of life and subsequent obesity in childhood could affect the way optimal infant weight gain is defined in countries where public health priorities are changing.