This study evaluates the temporal trends of the Body Roundness Index (BRI) among US adults and its association with all-cause mortality. The analysis is based on data from the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2018, involving 32,995 noninstitutionalized civilian residents. BRI, a measure that considers waist circumference and body height, was found to have increased from 4.80 to 5.62 over the study period, with a biennial change of 0.95%. The association between BRI and all-cause mortality followed a U-shaped pattern, with a 25% increased risk for those with BRI less than 3.4 and a 49% increased risk for those with BRI of 6.9 or greater compared to the middle quintile of 4.5 to 5.5. After adjusting for various confounding factors, the findings suggest that BRI may be a useful noninvasive screening tool for estimating mortality risk, particularly in identifying high-risk individuals. The study highlights the importance of visceral fat distribution in predicting mortality and provides evidence for the potential of BRI as a novel anthropometric measure in public health practice.This study evaluates the temporal trends of the Body Roundness Index (BRI) among US adults and its association with all-cause mortality. The analysis is based on data from the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2018, involving 32,995 noninstitutionalized civilian residents. BRI, a measure that considers waist circumference and body height, was found to have increased from 4.80 to 5.62 over the study period, with a biennial change of 0.95%. The association between BRI and all-cause mortality followed a U-shaped pattern, with a 25% increased risk for those with BRI less than 3.4 and a 49% increased risk for those with BRI of 6.9 or greater compared to the middle quintile of 4.5 to 5.5. After adjusting for various confounding factors, the findings suggest that BRI may be a useful noninvasive screening tool for estimating mortality risk, particularly in identifying high-risk individuals. The study highlights the importance of visceral fat distribution in predicting mortality and provides evidence for the potential of BRI as a novel anthropometric measure in public health practice.