To assess the trends in overweight and obesity in pre-school children in urban areas of Ho Chi Minh City (HCMC), Vietnam, over the period 2002 to 2005. Two cross-sectional studies were conducted in 2002 and 2005. Multistage cluster sampling was used in both surveys to select the subjects. Sociodemographic information was collected using a self-administered questionnaire given to parents in 2002 and using an interview-administered questionnaire to parents in 2005. Weight and height were measured using the same standard methods in both surveys. BMI (kg/m2) was calculated and overweight/obesity was defined using the age- and sex-specific BMI cut-off points proposed by the International Obesity Taskforce. Children aged 4 to 5 years, attending pre-schools in urban areas of HCMC, Vietnam, in 2002 (n 492) and 2005 (n 670). The prevalence of overweight and obesity almost doubled from 2002 to 2005 (21.4 % and 36.8 %, respectively). The increase was more evident in less wealthy districts than in wealthy districts. The proportion of boys classified as obese in 2005 (22.5 %) was three times that in 2002 (6.9 %). The prevalence of overweight and obesity has increased rapidly in children aged 4 to 5 years in urban areas, and especially in less wealthy districts, over a 3-year period. These results signal an urgent need for prevention programmes to control and reverse this rapid upward trend in overweight and obesity in young children in HCMC.