To estimate the prevalence, social patterning, treatment and control of hypertension among older people in the 10/66 Dementia Research Group developing country sites. Cross-sectional surveys of SBP, hypertension, and hypertension awareness, treatment and control among 17 014 people aged 65 years and over in eight urban and four rural sites in Latin America, India and China. Hypertension prevalence was higher in urban (range 52.6-79.8%) than rural sites (range 42.6-56.9%), and lower in men than women [pooled prevalence ratio 0.89, 95% confidence interval (CI) 0.85-0.93]. Educational attainment was positively associated with hypertension in rural and least-developed sites. Age-standardized morbidity ratios, compared to USA (100), were higher in urban sites in Cuba (105), Dominican Republic (109), and Venezuela (107), similar in Puerto Rico (105), urban Mexico (99) and urban India (101), and lower in urban (75) and rural (61) Peru, rural Mexico (81), urban (91) and rural (84) China and rural India (65). In most Latin American centres, and urban China just over one-third of those with hypertension were controlled (BP < 140/90). Control was poor in rural China (2%), urban India (12%) and rural India (9%). The proportion controlled, not compositional factors (age, sex, education and obesity), explained most of the between-site variation in SBP. Uncontrolled hypertension is common among older people in developing countries, and may rise further during the demographic and health transitions. It is a major determinant of population SBP level. Strengthening primary care to improve hypertension management is necessary for primary prevention.