BACKGROUND: Our purpose was to assess blood pressure (BP) and its relationship with body mass index (BMI) over a 15-year interval in the Seychelles, a rapidly developing country in the African region. METHODS: Two independent cross-sectional examination surveys were conducted in 1989 (n = 1081) and 2004 (n = 1255) using representative samples of the population age 25-64 years. RESULTS: Between 1989 and 2004, mean BP (mm Hg) decreased slightly (from 133/87 to 131/86 in men and from 127/82 to 124/81 in women), with little change in the age-standardized prevalence of high BP (BP >/=140/90 or current treatment; from 45% to 44% in men and from 34% to 36% in women). During this same time period, there were marked increases in awareness (from 42% to 64%), treatment (22% to 59%), and control (3% to 20%) among participants with high BP. The prevalence of overweight (BMI >/=25 kg/m) increased from 39% to 60%. Furthermore, the linear relationship between BMI and BP was markedly weaker in 2004 than in 1989, irrespective of antihypertensive treatment and age, and among both lean and overweight participants. Among untreated persons, a BMI increment of 1 kg/m was associated with an elevation of 2.0/1.5 mm Hg of systolic/diastolic BP in 1989 but only 1.3/1.0 mm Hg in 2004. CONCLUSIONS: The association between BMI and BP has decreased over time. Further study is needed to understand the reasons for the decline in this association, and what the implications are in the context of the obesity epidemic.