Debate continues on the limitations of using body mass index (BMI) to assign youth overweight/obesity status. Calculated as weight in kilograms divided by height in meters squared, BMI might not be applicable in youth during periods of rapid growth. Although recent evidence has indicated that triponderal mass index (TMI, calculated as weight in kilograms divided by height in meters cubed) might have better accuracy in estimating youth body fat levels than BMI,¹ its clinical importance in estimating adulthood outcomes has not been examined. Therefore, we assessed whether youth TMI and its combination with BMI or subscapular skinfold thickness (SST), compared with BMI alone, have better utility in estimating adult obesity-related outcomes.