Although it is known that triglyceride concentrations increase with adiposity, whether the same increase applies for different percentiles of the triglyceride distribution has not been reported. Therefore, physician-supplied triglyceride concentrations from 7288 male and 2326 female runners were divided into strata according to the body mass index (BMI) and circumferences of the waist, hip and chest. The percentiles of the triglyceride distribution within each stratum were used to determine the cross-sectional regression slope between adiposity and triglyceride levels at each triglyceride percentile. Compared to the 5th percentile of the triglyceride distribution, the rise in men's triglycerides at the 95th percentile per unit of adiposity was 14-fold greater for BMI, 7.8-fold greater for waist circumference, 3.6-fold greater for hip circumference, and 4.4-fold greater for chest circumference. The rise in women's triglyceride concentrations at the 95th percentile was 8-fold greater than at the 5th percentile for each kg/m(2) increase in BMI. These results suggest that the metabolic effects of adiposity on plasma triglycerides depend upon whether the concentrations are high or low. This contradicts statistical assumptions upon which prior studies of adiposity have based their analyses. We speculate that the reported greater increases in triglycerides per unit of adiposity in whites than blacks, in men than women, and in low-density lipoprotein (LDL) pattern B than A are all consistent with the relationships we observe. It remains to be verified whether these relationship also apply to less active populations.