South Asians, who represent one-quarter of the world’s population, are at high risk of type-2 diabetes. India alone has ~56 million people with T2D, the second highest number in the world. Conservative estimates based on population growth, ageing and rates of urbanisation show that T2D cases in India will increase to ~100 million by 2030. T2D prevalence is currently ~9% in rural India, ~18% in urban India, and ~22% amongst Indians living in Europe (compared to ~6% among Europeans). Similar patterns are observed among South Asians in Pakistan, Bangladesh, and Sri Lanka. Diabetes poses a massive clinical, economic and social burden among South Asian countries as well as in the European countries to which South Asians have emigrated in large numbers. Our general goal is to identify approaches to risk stratification and health promotion through lifestyle modification that are acceptable, effective and efficient for prevention of T2D in South Asian communities from diverse settings. To achieve this, the iHealth-T2D study will investigate whether intensive lifestyle modification vs usual care reduces risk of T2D (primary endpoint) amongst South Asians with i. central obesity; ii. pre-diabetes and iii. overall (with central obesity and / or obesity). In addition, we will investigate health gains amongst family members, and complete a health economic analysis to quantify the cost-effectiveness of screening by waist circumference vs HbA1c, and of lifestyle modification for prevention of T2D, on the Indian subcontinent and Europe. The study aims to recruit 3,600 South Asian men and women aged 40-70 years with i. central obesity (waist≥100 cm) and/or ii. pre-diabetes (HbA1c 6.0-6.4%) to the study (Index cases). Recruitment was carried out in India, Pakistan, Sri Lanka and UK. Index cases received either i. intensive lifestyle modification; or ii. usual care (Total N=3,670). Intensive lifestyle modification followed clinically accepted, evidence based strategies to achieve >7% reduction in weight through improved diet and increased physical activity, and was delivered as 9 face-face and 13 telephone contact sessions over 12 months. Participants re being followed annually for 3 years to ascertain. The primary analyses will determine the clinical and cost-effectiveness of intensive lifestyle modification vs usual care for prevention of T2D amongst South Asians with i. central obesity; ii. pre-diabetes or iii, overall. Secondary analyses will address behavioural, psychosocial, clinical, and biochemical measures similarly. Health economic analyses will take account of costs incurred by the government, and participants. Effectiveness will be measured in terms of screening numbers needed to identify one case of ‘high risk’ for developing diabetes, and numbers needed to treat to prevent or delay one case of diabetes. Sensitivity analysis will be undertaken to test the robustness of the analysis in terms of the cost inputs and health outcomes.