We assessed the prevalence of gastric bypass surgeries in the United States on the basis of data from the 1998 to 2002 National Hospital Discharge Survey. Between 1998 and 2002, rates (per 100 000 adults) increased significantly (P<.001): from 7.0 to 38.6. This observed increase in the rate of gastric bypass surgery for the treatment of obesity may be attributed in part to improvements in surgical technique, improved patient outcomes, and increased popularity of this procedure. The prevalence of obesity in the US population continues to increase, making obesity a major public health concern. Bariatric surgery has become a popular method of treating obesity, with gastric bypass surgery emerging as the most widely used of these surgical procedures. We used the National Hospital Discharge Survey, an annual probability sample of discharged patients from nonfederal, short-stay (average length of stay of fewer than 30 days), noninstitutional hospitals in the United States, to examine annual rates and patient characteristics associated with the gastric bypass procedure from 1998 to 2002. A detailed description of the sample design and data collection method of the National Hospital Discharge Survey has been published in detail elsewhere.