Circumferences of biceps, chest, waist, iliac crest, and thigh along with skinfolds over the triceps, biceps, subscapular, suprailiac and knee have been used to evaluate weight loss during two programs of weight reduction. 1) The interobserver variation was greater in obese patients than in lean ones, but there was no significant correlation between these variations in measurements and body weight. 2) Variability in measurement from week to week in obese patients at a stable weight was consistently larger for skinfold measurements than for circumferences. 3) The assessment of body fat using the sum of the skinfold measurements in four regions had a correlation of 0.94 with the calculation of body fat using height and weight. 4) In the first study of weight loss, relatively higher correlations were found between weight loss and changes in each of the circumferences than with changes in skinfold thickness. The subscapular skinfold was the only one that showed a good correlation with weight loss. 5) In the second study of weight loss, we attempted to improve reproducibility of sequential measurement of circumferences by measuring them each time at identical distances from the floor. In this study, the correlations were less satisfactory, suggesting that visual assessment of the “appropriate” region at which to measure the circumference of the waist, chest, and hips is better than a more rigidly defined one. 6) The use of skinfold calipers is not to be recommended in assessing or following obese patients. Neither of the available instruments has a sufficiently large grip to encompass the triceps or subscapular skinfold in many patients, and even when they do, the delineation of this skinfold is technically more difficult. In addition, the coefficient of variation for all skinfold measurements was substantially greater than for circumferences measured in the same subjects by the same observer.