['We study the impact of emergency department (ED) crowding on delays in treatment and nontreatment for patients with severe pain.', 'We performed a retrospective cohort study of all patients presenting with severe pain to an inner-city, teaching ED during 17 months. Poor care was defined by 3 outcomes: not receiving treatment with pain medication while in the ED, a delay (>1 hour) from triage to first pain medication, and a delay (>1 hour) from room placement to first pain medication. Three validated crowding measures were assigned to each patient at triage. Logistic regression was used to test the association between crowding and outcomes.', 'In 13,758 patients with severe pain, the mean age was 39 years (SD 16 years), 73% were black, and 64% were female patients. Half (49%) of the patients received pain medication. Of those treated, 3,965 (59%) experienced delays in treatment from triage and 1,319 (20%) experienced delays from time of room placement. After controlling for factors associated with the ED treatment of pain (race, sex, severity, and older age), nontreatment was independently associated with waiting room number (odds ratio [OR] 1.03 for each additional waiting patient; 95% confidence interval [CI] 1.02 to 1.03) and occupancy rate (OR 1.01 for each 10% increase in occupancy; 95% CI 0.99 to 1.04). Increasing waiting room number and occupancy rate also independently predicted delays in pain medication from triage (OR 1.05 for each waiting patient, 95% CI 1.04 to 1.06; OR 1.18 for each 10% increase in occupancy; 95% CI 1.15 to 1.21) and delay in pain medication from room placement (OR 1.02 for each waiting patient, 95% CI 1.01 to 1.03; OR 1.06 for each 10% increase in occupancy, 95% CI 1.04 to 1.08).'] Is emergency department crowding associated with poor care for patients with severe pain?