The present community study describes the nature of relationship between blood pressure and body mass index (BMI) in relation to sociodemographic factors among the Khasi mothers of Sohra (Cherrapunji), Meghalaya, India. It was found that older mothers were significantly heavier than younger mothers in terms of both body weight (p < 0.01) and BMI (p < 0.01), and the relation between age and BMI was positively significant (p < 0.01). The prevalence of underweight was about 15% and 12% among the younger and older mothers, respectively; whereas the prevalence of overweight exceeded that of underweight, and it was statistically higher (p < 0.01) in older mothers (34%) than in their younger counterparts (25%). The prevalence of hypotension was about 16% among mothers below 30 years old, which was significantly higher than among older mothers (p < 0.001). However, older mothers had a higher prevalence of prehypertension and hypertension compared to younger mothers (p < 0.001). The marginal effects of socioeconomic status on age-adjusted blood pressure in terms of household income and educational levels were not statistically significant. The regression analysis indicated a non-linear relationship between BMI and blood pressure. It was found that younger women had on average lower age-adjusted blood pressure than those with normal BMI. However, the effect of being underweight on age-adjusted blood pressure disappeared when overweight was included in the model, indicating that overweight women had on average higher age-adjusted blood pressure than underweight women in the present study. Therefore, it is likely that the positive correlation between BMI and blood pressure may predominantly be due to elevated blood pressure at higher BMI levels, especially in populations with decreasing proportion of underweight due to a rapid increase in overweight and obesity. Our findings may also have certain implications for the relation between underweight and other adverse health outcomes of undernutrition in less developed countries.