The study was done to find out the association between mid-upper arm circumference (MUAC) and body mass index (BMI) and to estimate the cut-off values of MUAC in elderly. Methods: A community-based cross-sectional study was done in a resettlement colony in Delhi. Persons aged 60 years and above were selected by cluster random sampling. House-to-house visits were made, and weight, arm span, mid-upper-arm circumference were measured. Mid-upper arm circumference and body mass index of participants are expressed as mean ± standard deviation (SD). Scatter diagrams and regression lines were plotted to study the relationships. Receiver operating characteristics (ROC) analysis was done and area under ROC curve was assessed. The sensitivity and specificity for different values of mid-upper arm circumference was calculated. Results: 711 elderly persons were recruited. Positive correlation was seen between BMI and MUAC in men and women (r=0.76), with 0.67 in men and 0.76 in women (p<0.001). Cut-off values for detecting undernutrition were explored by ROC. In men, 25.7 cm yielded sensitivity and specificity of 80.2% and 78.6% respectively, AUC (95%CI) was 0.85 (0.80, 0.90). In women, with a cut-off 24.3 cm both the sensitivity and specificity were 79%, AUC (95%CI) was 0.86(0.81, 0.91). Conclusion: The study authenticates that MUAC correlates positively and significantly with BMI. MUAC values of 25.7 cm in men and 24.3 cm in women are useful cut-off points for undernutrition, while 28.5 cm in men and 27.5 cm in women could be useful for overweight/obesity.