BACKGROUND: Studies in Western populations report a J- or U-shaped relation between body mass index (BMI; in kg/m(2)) and mortality, in which persons with extremes of BMI experience increased mortality. In contrast, little is known about populations in developing countries, where nutritional status is lower. OBJECTIVE: The objective was to examine the association between BMI and mortality in Bangladeshi women. DESIGN: A cohort of 1888 rural Bangladeshi women (mean age: 27.9 y) was followed over 19 y. Height, weight, arm circumference, fertility, and socioeconomic data were obtained between 1975 and 1979. Mortality, loss-to-follow-up, and additional socioeconomic data were identified by the demographic surveillance system of the International Centre for Health and Population Research, Bangladesh. Proportional hazards regression was used to examine the relation between BMI and all-cause mortality. RESULTS: The association between BMI and mortality was reverse J-shaped. After adjustment for socioeconomic indicators, the risk of dying was highest in women with BMIs in the lowest 10% of the decile distribution (< 16.39) and lowest in women with intermediate (11-89% range of the decile distribution) BMIs (16.39-20.71). Women with BMIs in the highest 10% of the distribution (> 20.71) had slightly elevated mortality (NS) compared with those with intermediate BMIs. Age and education were strongly associated with mortality. Women without schooling had a risk of mortality 4 times that of women with > or = 1 y of schooling. CONCLUSIONS: A woman's BMI relative to the BMI distribution in the local population may be a better predictor of mortality than is absolute BMI. The contribution of education in reducing mortality supports development programs aimed at increasing women's education.