Among countries which have undergone a rapid socio-economic and nutrition transition over the past few decades, the Indian Ocean island of Mauritius is among those with the greatest surge in the prevalence of type 2 diabetes and CVD. The aim of the present study was to characterise the BMI and cardiovascular functions of children and adolescents of this at-risk population. Data were collected through measurements of anthropometry, resting heart rate and blood pressure in a nationally representative sample (n 2489) of children (5–10 years) and adolescents (11–18 years), and analysed according to sex and ethnic identity: South Asian Hindus and Muslims (both of Indian ancestry), Creole (of varying degrees of African ancestry) and Chinese (of mainland China ancestry). Based on standards of the WHO or International Obesity Task Force, one in six of these young individuals exhibit a high BMI-for-age. Analysis by ethnicity revealed that Creole males and females show higher BMI-for-age but also lower heart rate (P < 0·001) even after adjustment for BMI. Additionally, Chinese males and females show higher systolic blood pressure (P < 0·01), independently of BMI. None of these ethnic differences could be related to household income, diet type (vegetarian v. non-vegetarian) or to fruit consumption. This study in children and adolescents of this multi-ethnic at-risk population for CVD reveal ethnic differences in BMI-for-age as well as consistent BMI-independent ethnic differences in heart rate and systolic blood pressure. These findings underscore the need to establish the BMI–fat % relationship across the various ethnic groups and for more detailed investigations about their differences in lifestyle and dietary habits that might explain their differential cardiovascular functions prior to adulthood.