A radiological method for assessment of obesity is described. A radiograph of the soft tissues of the upper arm is obtained and the subcutaneous fat layer measured. The results obtained by this method have been compared with those using a skinfold caliper and with the ponderal index, calculated from the height and weight of the subject. A highly significant correlation was found. The radiological method has several advantages: it leaves a permanent record, it is accurate in obese persons when the skinfold caliper cannot be used, and unlike the ponderal index it is not influenced by weight increases due to causes other than fat accumulation.