The purpose of this study was to investigate the importance of familial aggregation in abdominal visceral fat (AVF) level as assessed by computed tomography (CT). Four measures of abdominal adipose tissue, obtained from an abdominal scan between the fourth and fifth Lumbar vertebrae (L4-L5) taken in 366 adult subjects from 100 French-Canadian nuclear families, were considered in this study. Total abdominal fat, AVF, subcutaneous abdominal fat, obtained by computing the difference between total and AVF tissue areas, and the visceral to total abdominal fat ratio were measured. Spouses, parent- offspring, and sibling correlations were computed by maximum likelihood methods after adjustment of the four phenotypes for age and for age and total fat mass (FM) derived from underwater weighing. Significant familial aggregation was found for all phenotypes, whether adjusted or not for body FM. However, after adjustment of data for body FM, in addition to age, all spouse correlations became nonsignificant, suggesting that the familial aggregation of abdominal fat is primarily genetic. Heritability estimates reached 42% and 56% for subcutaneous fat and AVF, respectively. These results suggest that genetic factors are major determinants of the familial aggregation observed in the amount of abdominal fat, irrespective of total body fat content, and that AVF seems more influenced by genetic factors than abdominal subcutaneous adipose tissue. These findings imply that some individuals are more at risk than others to exhibit the various metabolic complications associated with upper-body obesity because of their inherited tendency to store abdominal fat in the visceral depot rather than in the subcutaneous depot.