This study evaluated the temporal trends of the body roundness index (BRI) and its association with all-cause mortality among US adults from 1999 to 2018. The BRI, a new anthropometric measure, reflects body fat distribution more comprehensively than traditional measures like BMI. The study analyzed data from 32,995 US adults, with a mean BRI increasing from 4.80 to 5.62 over the 20-year period, showing a biennial increase of 0.95%. A U-shaped association was found between BRI and all-cause mortality, with the lowest and highest BRI groups having significantly increased mortality risks. Adults with BRI less than 3.4 had a 25% higher risk of death, while those with BRI of 6.9 or higher had a 49% higher risk compared to those in the middle quintile (4.5-5.5). The study highlights the importance of BRI as a noninvasive tool for assessing mortality risk, particularly in women, older adults, and Mexican Americans. The findings suggest that BRI could be incorporated into public health practice for risk assessment and management. The study also notes that BRI trends align with the rising prevalence of obesity and central adiposity in the US. However, limitations include potential nonresponse bias and the lack of disease-specific mortality data. Overall, the study provides evidence for BRI as a promising indicator for mortality risk estimation.This study evaluated the temporal trends of the body roundness index (BRI) and its association with all-cause mortality among US adults from 1999 to 2018. The BRI, a new anthropometric measure, reflects body fat distribution more comprehensively than traditional measures like BMI. The study analyzed data from 32,995 US adults, with a mean BRI increasing from 4.80 to 5.62 over the 20-year period, showing a biennial increase of 0.95%. A U-shaped association was found between BRI and all-cause mortality, with the lowest and highest BRI groups having significantly increased mortality risks. Adults with BRI less than 3.4 had a 25% higher risk of death, while those with BRI of 6.9 or higher had a 49% higher risk compared to those in the middle quintile (4.5-5.5). The study highlights the importance of BRI as a noninvasive tool for assessing mortality risk, particularly in women, older adults, and Mexican Americans. The findings suggest that BRI could be incorporated into public health practice for risk assessment and management. The study also notes that BRI trends align with the rising prevalence of obesity and central adiposity in the US. However, limitations include potential nonresponse bias and the lack of disease-specific mortality data. Overall, the study provides evidence for BRI as a promising indicator for mortality risk estimation.