The relationship between physique and metabolic fitness was examined in a sample of 413 boys and 343 girls 9-18 years of age from Phase I of the Quรฉbec Family Study. Physique was assessed using the Heath-Carter anthropometric somatotype. Indicators of metabolic fitness were plasma triglyceride levels (TG), high density lipoprotein cholesterol (HDL-C), low density lipoprotein cholesterol (LDL-C), and blood glucose levels (GLY). The sample was divided into three age groups, 9-12, 13-15, and 16-18 years of age. A partial canonical correlation analysis was used to quantify the relationship between the standardized somatotype and metabolic fitness variables (z-transformed) with age as the covariate. In both boys and girls the first canonical correlation is significant (P โฉฝ 0.001) and indicates a relationship between the physique and metabolic fitness variables. By age group, the 16-18 year old boys, and the 9-12, 13-15, 16-18 year old girls demonstrate significant canonical correlations (P โฉฝ 0.03). Overall, 8% to 19% of the variance in metabolic fitness can be explained by the Heath-Carter anthropometric somatotype. The makeup of the canonical variates is similar for all age groups. Generally, the physique domain is characterized by a positive loading for ectomorphy and negative loadings for endomorphy and mesomorphy. The metabolic fitness domain has a positive loading for HDL-C and negative loadings for TG, LDL-C, and GLY. The results suggest that in youth 9-18 years, a physique characterized by high endomorphy and mesomorphy is associated with higher levels of TG, LDL-C, and GLY, and lower levels of HDL-C. Am. J. Hum. Biol. 10:341-350, 1998. ยฉ 1998 Wiley-Liss, Inc.