A cross-sectional study was undertaken to determine the anthropometric profile and nutritional status of adult Kora Mudis, a tribal population of Bankura District, West Bengal, India, based on their body mass index (BMI). A total of 500 adult (18.0 < age ≤ 65.0 years) Kora Mudis from two villages (Phulberia and Siromonipur, approximately 160 km from Kolkata) were studied. Anthropometric measurements, including height, weight, circumferences, and skinfolds, were measured using standard protocols. BMI was calculated and utilized as a measure of nutritional status. The extent of undernutrition (BMI < 18.5) was found to be very high (52.2%). The frequency of undernutrition was higher in women (56.4%) than men (48.0%), although this difference was not statistically significant. Using the World Health Organization criterion, the prevalence of undernutrition is classified as ‘very high’. In order to fully understand the causes and consequences of adult undernutrition, further research is needed not only among this ethnic group but also on the other tribal populations of India.