OBJECTIVE To examine time trends (study 1) and sociocultural factors associated with childhood overweight (study 2) in La Reunion Island. METHODS Study 1: a longitudinal analysis of anthropometric data available from health services in the town of Saint-Pierre. Study 2: a case - control study. METHODS Study 1: 1753 children born between 1977 and 1996. Study 2: 101 six-year old overweight children sex-matched with 101 non-overweight children. METHODS Study 1: overweight at birth (birth weight>4 kg) and at age 4 and 6 using French references and references from the International Obesity Task Force. Study 2: parental and perinatal data, child's lifestyle and representation of food, all collected from the mother. RESULTS Study 1: a dramatic increase in the prevalence rate of overweight at 4 and at 6 is observed, more severe in girls. Study 2: multivariate logistic regressions showed that mother's overweight was the only variable significantly associated with overweight in both the sexes. The other associated factors were related to sociocultural and family features and sedentarity. Logistic probability functions derived from these data are proposed as a tool for detection of at risk families. CONCLUSIONS Our results show the need for a targeted prevention of overweight. We offer a proposal based on education and behaviour modification in La Reunion Island.