Bangladesh is currently going through a nutritional transition with rapid increase in overnutrition while undernutrition is still remaining prevalent. Nevertheless, population-based data on demographic, socioeconomic and lifestyle factors associated with underweight and overweight among adult population is scarce. Employing a nationwide cross-sectional survey, we collected anthropometric, demographic, socioeconomic , lifestyle and dietary information from 12,180 adults aged ≥35 years. Body Mass Index (BMI) was calculated using standard formula and categorized into underweight (<18.50), normal weight (18.50-22.99), and overweight (≥23.00). Multivariable multinomial logistic regression was performed to identify factors associated with underweight and overweight. Overall, prevalence of underweight and overweight was 18.1% (95% CI: 17.5-18.8) and 33.7% (95% CI: 32.9-34.6), respectively. All the demographic, socioeconomic , dietary and lifestyle factors showed significant association with nutritional status in bivariate analysis. In adjusted analysis, factors showing significant positive association with underweight included female gender (ARRR-1.38, 95% CI: 1.11-1.71), older age [compared to 35-39 years age group, ARRR (95% CI) for ≥ 70 years is 2.32 (1.89-2.86), for 60-69 years is 1.62 (1.36-1.93), for 50-59 years 1.34 (1.13-1.58) and for 40-49 years 1.05 (0.87-1.15)] and smoking habit (ARRR-1.32, 95% CI: 1.14-1.52) while factors showing significant inverse association with underweight included higher household wealth [compared to lowest wealth quintile, ARRR (95% CI) for highest quintile is 0.68 (0.55-0.84), for second highest quintile 0.77 (0.65-0.91), for middle quintile 0.81 (0.69-0.94) and for second lowest quintile 0.89 (0.77-1.03)], urban residence (ARRR-0.66, 95% CI: 0.66-0.90), and more frequent meat/fish and fruits consumption (ARRR-0.76, 95% CI: 0.65-0.90). On the other hand, factors significantly associated with increased risk of overweight included female gender (ARRR-1.35, 95% CI: 1.12-1.63), higher household wealth [compared to lowest wealth quintile, ARRR (95% CI) for highest quintile is 2.27 (1.93-2.68), for second highest quintile 1.67 (1.44-1.94), for middle quintile 1.26 (1.10-1.46) and for second lowest quintile 1.07 (0.93-1.24), excess food availability [compared to food shortage, ARRR (95% CI) for excess food in the household is 1.29 (1.12-1.47) and for no shortage/no excess is 1.23 (1.09-1.38) and more frequent fruits consumption [compared to no fruits, ARRR (95% CI) for 5-7 days per week consumption is 1.61 (1.41-1.83) and for 3-4 days per week is 1.28 (1.16-1.41) and factors significantly associated with decreased risk of overweight included older age [compared to 35-39 years age group, ARRR (95% CI) for ≥ 70 years is 0.77 (0.64-0.93), for 60-69 years is 0.82 (0.71-0.94), for 50-59 years 0.91 (0.80-1.04) and for 40-49 years 1.01 (0.89-1.15)] and smoking (ARRR-0.76, 95% CI: 0.68-0.86). Both underweight and overweight are prevalent in Bangladeshi adult population. Several demographic, socioec...