BACKGROUND The influence of age and sex on the distribution of abdominal adipose tissue for a given waist circumference (WC) is unclear. OBJECTIVE The objective was to investigate the influence of age and sex on total (TAAT), visceral (VAT), and abdominal subcutaneous (ASAT) adipose tissue for a given WC. DESIGN Body composition was assessed by whole-body magnetic resonance imaging in 147 younger men (< 50 y), 83 older men, 171 younger (premenopausal) women, and 80 older (postmenopausal) women with a wide range (16-40; in kg/m(2)) of body mass indexes. RESULTS Within each sex, the regression lines between WC and TAAT were not significantly different (P > 0.1) between younger and older groups. Collapsed across age groups, women had more TAAT for a given WC than did men; however, this difference was significantly reduced with increasing WC (P < 0.05). Within each sex, regression lines derived for WC and ASAT were not significantly different between younger and older groups (P > 0.1). Collapsed across age groups, women had 1.8 kg more ASAT for a given WC (P < 0.05) than did men across the range of WCs. Within each sex, older men and women had a significantly greater increase in VAT for a given WC (P < 0.05) than did younger men and women. Furthermore, independent of age group, the slopes for WC and VAT were significantly higher (P < 0.05) in men than in women. CONCLUSIONS There are significant sex differences in TAAT, VAT, and ASAT for a given WC. Furthermore, the relation between WC and VAT is substantially influenced by age.