Both the amount and quality of dietary fat have been implicated in the pathogenesis of obesity. Adipose tissue fatty and composition, which is known to reflect dietary intake, was sampled in 413 free-living, healthy American males appearing for a routine medical examination. The average age was 46.8 +/- 11.4 years (mean +/- s.d.) and body mass index (BMI)--weight/height--was 25.2 +/- 3.4. The BMI was correlated (P less than 0.01) with known risk factors for cardiovascular disease as follows: total cholesterol (TC) r = 0.18, triglycerides (TG) r = 0.32, low-density lipoprotein cholesterol (LDL-C) r = 0.18, high-density lipoprotein cholesterol (HDL-C) r = -0.24, systolic and diastolic blood pressure (BP) r = 0.30. Underlying patterns which might be related to diet were sought in the distribution of the seven major fatty acids in adipose tissue. Statistical analysis permitted delineation of three factors which were hypothetically related to animals fat intake (F1--monounsaturates), carbohydrate intake (F2--saturates) and vegetable oil intake (F3--polyunsaturates). F1 and F3 together accounted for 12 percent of the variance in BMI while F2 had no influence. Our conclusions are that the variance in BMI is related much more to non-dietary factors than to adipose tissue fatty acid composition and that the nature of dietary fat was not a major distinguishing factor in obesity in this population. There was also no evidence for a high dietary carbohydrate (low fat) intake in the obese.