The National Animal Health Monitoring System (NAHMS) is sponsored by the USDA:APHIS: Veterinary Services (VS). The NAHMS Feedlot '99 Study included feedlots of 1000-head or greater capacity from the 12 leading cattle feeding states. Feedlots included in the study represented 84.9 percent of U.S. feedlots of this size and contained 96.1 percent of the U.S. feedlot cattle inventory on feedlots with 1000-head or greater capacity as of January 1, 2000. For the purposes of the study, operations were grouped into two size categories: those with capacities of between 1000 and 7999 head, and those with capacities of 8000 head or more. Beef animals were the main type of cattle placed in feedlots regardless of operation size. Approximately one-half of the placements in small and large operations were steers and heifers greater than 700 pounds. The largest source of cattle for small operations was directly from auction markets (46.9 percent of cattle). For large operations, the largest percentage (44.1 percent) of cattle was acquired through custom feeding, either by agreement with another party or via joint ownership with the feedlot. Almost all (97.8 percent) operations that processed cattle administered vaccines to aid in the prevention of respiratory disease. Most operations that processed cattle after arrival (68.0 percent) made some adjustments to processing procedure based on attributes of arriving cattle. Adjustment was more common in large operations (72.7 percent) than in small operations. A greater percentage (80.0 percent) of steers and heifers weighing less than 700 lbs. at the time of placement received more than one implant as compared with those weighing 700 lbs. or more at the time of placement (30.4 percent). Greater than 95 percent of operations considered each of the following quality assurance programs very or somewhat important: location of injections, route of injections, implanting strategy, antimicrobial selection, and measures to avoid residues. Contact for this paper: Lindsey Garber.