The waist-to-height ratio is an anthropometric measure of central adiposity that has emerged as a significant predictor of cardiovascular disease risk factors in children and adolescents. However, the simple waist-to-height ratio retains residual correlation with height, which could cause the measure to over- or under-adjust for the effect of height at certain ages. We investigated the dependence of waist-to-height ratio on height in the representative US National Health and Nutrition Examination Survey 1999-2004. We stratified 11 270 subjects aged 2-18 years by age and sex. There was considerable residual correlation between height and the waist-to-height ratio, ranging from -0.29 to 0.36. Thus, simply dividing waist circumference by height (WC/Ht1) might not be appropriate to "adjust for height" during periods of growth. We fitted a log-log regression of waist circumference on height to determine which exponent for height ensures that the log of the ratio is uncorrelated with the log of height, which we call the optimal exponent for WC/Ht(p). This optimal power for height in the age- and sex-specific waist-to-height ratio varies from 0.5 to 2.0, with similar patterns for males and females. The value peaks at age 8, and is close to 1 at age 18. Future research should investigate how this affects relationships between central adiposity and cardiovascular disease risk factors across these ages, and how using a power other than 1 might reduce bias and improve precision.