This study was undertaken to update and revise the estimate of the economic impact of obesity in the United States. A prevalence-based approach to the cost of illness was used to estimate the economic costs in 1995 dollars attributable to obesity for type 2 diabetes mellitus, coronary heart disease (CHD), hypertension, gallbladder disease, breast, endometrial and colon cancer, and osteoarthritis. Additionally and independently, excess physician visits, work-lost days, restricted activity, and bed-days attributable to obesity were analyzed cross-sectionally using the 1988 and 1994 National Health Interview Survey (NHIS). Direct (personal health care, hospital care, physician services, allied health services, and medications) and indirect costs (lost output as a result of a reduction or cessation of productivity due to morbidity or mortality) are from published reports and inflated to 1995 dollars using the medical component of the consumer price index (CPI) for direct cost and the all-items CPI for indirect cost. Population-attributable risk percents (PAR%) are estimated from large prospective studies. Excess work-lost days, restricted activity, bed-days, and physician visits are estimated from 88,262 U.S. citizens who participated in the 1988 NHIS and 80,261 who participated in the 1994 NHIS. Sample weights have been incorporated into the NHIS analyses, making these data generalizable to the U.S. population. The total cost attributable to obesity amounted to $99.2 billion dollars in 1995. Approximately $51.64 billion of those dollars were direct medical costs. Using the 1994 NHIS data, cost of lost productivity attributed to obesity (BMI> or =30) was $3.9 billion and reflected 39.2 million days of lost work. In addition, 239 million restricted-activity days, 89.5 million bed-days, and 62.6 million physician visits were attributable to obesity in 1994. Compared with 1988 NHIS data, in 1994 the number of restricted-activity days (36%), bed-days (28%), and work-lost days (50%) increased substantially. The number of physician visits attributed to obesity increased 88% from 1988 to 1994. The economic and personal health costs of overweight and obesity are enormous and compromise the health of the United States. The direct costs associated with obesity represent 5.7% of our National Health Expenditure in the United States.