Childhood obesity is a serious health problem and prevalence increases dramatically around the world, including Sweden. The aim of the current thesis was to examine parents’ and children’s stress in relation to childhood obesity. Parenting stress, social support, parental worries, and serious life events, as well as children’s temperament, self-esteem, body dissatisfaction, saliva cortisol, weight and height were measured to estimate stress and the relation between stress and childhood obesity. Data was collected as part of the cohort project All Babies in Southeast Sweden (ABIS) which main aim is to understand the causes of Type 1 Diabetes. All 21700 children born between October 1997 and October 1999 in Southeast Sweden and their parents were invited to participate and questionnaires were completed for 16070 children at birth. Questionnaires were then collected at follow-ups at 1 year (N=11078), at 2-3 years (N=8803), at 5-6 years (N=7443), and at 8 years (N=3959). The main findings were a relation between parents’ psychological stress and lower self-esteem of children, a relation between parenting stress and higher cortisol levels of children, and a relation between children’s body dissatisfaction and lower self-esteem. Another main finding was a relation between cumulative psychological stress and an increased prevalence of childhood obesity. The current thesis summarized these results, found good validity of the instruments, and the analyses did not indicate any systematic attrition due to stress. It is concluded that the psychological variables reported by parents can be used as proxies for children’s experience of stress in epidemiological studies such as ABIS, and that psychological stress seems to be a contributing factor in childhood obesity. This relation needs to be studied further in order to better understand and intervene in the current epidemic of childhood obesity. These findings may also help to better examine if psychological stress and childhood obesity are contributing factors in the etiology of Type 1 Diabetes.