Context: National quality improvement initiatives implemented in the late 1990s were followed by substantial increases in opioid prescribing in the United States, but it is unknown whether opioid prescribing for treatment of pain in the emergency department has increased and whether differences in opioid prescribing by race/ethnicity have decreased. Objectives: To determine whether opioid prescribing in emergency departments has increased, whether non-Hispanic white patients are more likely to receive an opioid than other racial/ethnic groups, and whether differential prescribing by race/ethnicity has diminished since 2000. Design and Setting: Pain-related visits to US emergency departments were identified using reason-for-visit and physician diagnosis codes from 13 years (1993-2005) of the National Hospital Ambulatory Medical Care Survey. Main Outcome Measure: Prescription of an opioid analgesic. Results: Pain-related visits accounted for 156 729 of 374 891 (42%) emergency department visits. Opioid prescribing for pain-related visits increased from 23% (95% confidence interval [CI], 21%-24%) in 1993 to 37% (95% CI, 34%-39%) in 2005 (P<.001 for trend), and this trend was more pronounced in 2001-2005 (P=.02). Over all years, white patients with pain were more likely to receive an opioid (31%) than black (23%), Hispanic (24%), or Asian/other patients (28%) (P<.001 for trend), and differences did not diminish over time (P=.44), with opioid prescribing rates of 40% for white patients and 32% for all other patients in 2005. Differential prescribing by race/ethnicity was evident for all types of pain visits, was more pronounced with increasing pain severity, and was detectable for long-bone fracture and nephrolithiasis as well as among children. Statistical adjustment for pain severity and other factors did not substantially attenuate these differences, with white patients remaining significantly more likely to receive an opioid prescription than black patients (adjusted odds ratio, 0.66; 95% CI, 0.62-0.70), Hispanic patients (0.67; 95% CI, 0.63-0.72), and Asian/other patients (0.79; 95% CI, 0.67-0.93). Conclusion: Opioid prescribing for patients making a pain-related visit to the emergency department increased after national quality improvement initiatives in the late 1990s, but differences in opioid prescribing by race/ethnicity have not diminished. ©2008 American Medical Association. All rights reserved.