Study Objective: We analyzed 980 emergency department visits for 951 patients with managed care insurance to document gatekeeping interactions and compare ED coding with professional fee billing reimbursements. Methods: A prospective cohort study was performed at 12 academic and community hospital EDs in 4 states involving consecutive ED patients with managed care insurance. The main outcomes measured were gatekeeper decisions, coding levels, and reimbursement. Results: Preauthorization for payment was required from managed care gatekeepers for 876 (89%) patients. Authorization was granted for 490 (56%) of these visits and denied in 176 (20%) visits; gatekeepers were not available for 210 (24%) visits. Reimbursement was initially denied for 211 (43%) of the ED visits preapproved by managed care gatekeepers. Reimbursement was initially denied for most (634 or 65%) visits, and downcoding occurred in the other 346 (35%) visits. Appeals for 560 (57%) visits resulted in a decrease in the number of unreimbursed ED visits to 193 and an increase in the number of reimbursed ED visits to 787. Conclusion: Preauthorization gatekeeping is not predictive of whether managed care third-party payers will initially reimburse ED visits. Overall, almost two thirds of all ED claims were initially denied, and reimbursed claims were uniformly downcoded. On appeal, reimbursement was often reinstated or increased, although billing services only appealed about half of ED visits. [Young GP, Ellis J, Becher J, Yeh C, Kovar J, Levitt MA. Managed care gatekeeping, emergency medicine coding, and insurance reimbursement outcomes for 980 emergency department visits from four states nationwide. Ann Emerg Med. January 2002;39:24-30.]