OBJECTIVE: To identify the risk factors of obesity in preschool children in China. DESIGN: A nationwide case-control study in eight cities in China. SUBJECTS: A total of 748 boys and 574 girls (age 0.1 - 6.9 y), including the obese and non-obese. One obese child was matched with one non-obese child by sex and age. MEASUREMENTS: Weight, height and other measurements were taken for all the subjects. The information on child activity, feeding pattern and family background was collected by our study team from the parents and the kindergarten teacher. RESULTS: Birth weight greater than or equal to 4.0 kg, high eating speed, obesity among the child's relatives greater than or equal to 25%, mother's body mass index (BMI) > 25 kg/m(2) and father's BMI > 25 kg/m(2) were identified as the major significant (P < 0.05) risk factors of obesity in preschool children in China. CONCLUSION: Family history of obesity, high birth weight and eating speed were identified as the risk factors of obesity in preschool children in China. Our results show the need for family therapy as part of an intervention program for childhood obesity, which includes behavior modification.