The family environment can contribute to the development of obesity. Parenting styles may influence the development of food preferences and the ability of a child to regulate intake. Parents and other family members arrange a common, shared environment that may be conducive to overeating or a sedentary lifestyle. Family members serve as models, and reinforce and support the acquisition and maintenance of eating and exercise behaviours. Family-based interventions are needed to modify these variables in treating obese children. We have made significant progress in developing interventions that target obese 8-12 year-old children, completing four 10-year follow-up studies that provide support for two factors that are useful in childhood obesity treatment. First, our research suggests that the direct involvement of at least one parent as an active participant in the weight loss process improves short- and long-term weight regulation. Second, our research suggests that increasing activity is important for maintenance of long-term weight control. Correlational analyses on the 10-year database suggest that family and friend support for behaviour change are related to long-term outcome. Family-based obesity treatment provides interventions for both children and their parents, but children benefit more from treatment than their parents. These positive results provide an encouraging basis for optimism that further development of interventions, based on newer research on family processes and behaviour changes, can be useful in treating childhood obesity.