The reliability of single measurements of waist and hip circumference and the ratio of waist circumference to hip circumference (a widely used measure of body fat distribution) has not been fully examined. The authors analyzed measurements of waist and hip circumference, as well as self-reported weight and height, repeated 3-6 times between 1986 and 1991 among 1,851 participants in the New York University Women's Health Study. Quetelet index (weight (kg)/height (m)2) was positively correlated with waist circumference (r = 0.88), hip circumference (r = 0.89), and waist/hip ratio (r = 0.52). Mean weight was positively correlated with the within-subject variance of waist circumference (r = 0.27) and, to a lesser degree, with the within-subject variance of hip circumference (r = 0.08) and waist/hip ratio (r = 0.10). The within-subject variance of weight was positively correlated with the within-subject variance of waist (r = 0.30) and hip (r = 0.23) measurements, and less so with waist/hip ratio (r = 0.05). Intraclass correlations for waist, hip, and waist/hip ratio were 0.89, 0.81, and 0.74, respectively; adjustment for Quetelet index reduced the intraclass correlations for waist and hip measures by 33% and 48%, respectively. Such adjustment can provide a more realistic determination of the reliability associated with an exposure variable in the design and analysis of studies investigating the relation between body fat distribution and disease.