Data from a predominantly urban sample of 116 men and 130 women aged 25-64 years and collected in 1984/85 as a part of the Swiss WHO MONICA project, were analysed cross-sectionally to study the interrelationship between relative weight, subcutaneous fat and fat distribution, as well as the dependence of these anthropometric characteristics on behavioral and sociodemographic factors. Skinfold thicknesses were found to increase with age almost linearly in women, while in men they increased only before age 40 to 45. Subcutaneous fat was, but fat distribution was not, highly correlated with relative weight in both sexes. Alcohol consumption, healthy dietary habits (inversely), and exercise (inversely) were all significantly related to subcutaneous fat in men, while the relatively strongest predictors of female skinfold thicknesses were smoking (inversely), coffee consumption, and education (inversely). In multivariate analysis, environmental factors explained up to 10% of skinfold variance in male subjects and between 10 and 15% in females. Fat distribution was more influenced by environmental factors in men (about 8% of explained variance) than in women (about 4%). In men, truncal fat depended more on lifestyle that did upper arm fat, with smoking (directly) and exercise (inversely) being relatively most predictive of abdominal fat. We conclude that, although relative weight, subcutaneous fat, and fat distribution correlate intra-individually, they are not equivalent and interchangeable anthropometric characteristics. This is reflected by the varying associations of the three fatness indicators with age and environmental factors such as smoking, diet, exercise, and education. Gender seems to be an important modifying factor of environment-body fat-associations.(ABSTRACT TRUNCATED AT 250 WORDS)