The pace of research on the causes and consequences of obesity has increased dramatically since the late 1990s. However, a great chasm exists between the high-quality measurements of fatness used in the medical literature and the mostly self-reported height and weight data found in social science surveys. This article discusses the scientific value of including more accurate measures of fatness in the Panel Study of Income Dynamics (PSID). It describes why fatness and obesity are of interest to PSID users, the concepts they measure, the strengths and weaknesses of alternative biomeasures for these concepts, the value added of including each in the PSID, and their synergies with the PSID structure. Although no single measure of fatness is ideal for every situation, given scarce PSID resources we recommend adding waist circumference, percentage of body fat, total body fat, and fat free mass through a method such as bioelectrical impedance analysis, as well as determining genetic predisposition to obesity.