Inappropriate use of antibiotics for acute respiratory tract infections (ARTIs) has decreased in many outpatient settings. For patients presenting to U.S. emergency departments (EDs) with ARTIs, antibiotic utilization patterns are unclear. We conducted a retrospective cohort study of ED patients from 2001 to 2010 using data from the National Hospital Ambulatory Medical Care Survey (NHAMCS). We identified patients presenting to U.S. EDs with ARTIs and calculated rates of antibiotic utilization. Diagnoses were classified as antibiotic appropriate (otitis media, sinusitis, pharyngitis, tonsillitis, and nonviral pneumonia) or antibiotic inappropriate (nasopharyngitis, unspecified upper respiratory tract infection, bronchitis or bronchiolitis, viral pneumonia, and influenza).There were 126 million ED visits with a diagnosis of ARTI, and antibiotics were prescribed in 61%. Between 2001 and 2010, antibiotic utilization decreased for patients aged<5 presenting with antibiotic-inappropriate ARTI (rate ratio [RR], 0.94; confidence interval [CI], 0.88 to 1.00). Utilization also decreased significantly for antibiotic-inappropriate ARTI patients aged 5 to 19 years (RR, 0.89; CI, 0.85 to 0.94). Utilization remained stable for antibiotic-inappropriate ARTI among adult patients aged 20 to 64 years (RR, 0.99; CI, 0.97 to 1.01). Among adults, rates of quinolone use for ARTI increased significantly from 83 per 1,000 visits in 2001 to 2002 to 105 per 1,000 in 2009 to 2010 (RR, 1.08; CI, 1.03 to 1.14). Although significant progress has been made toward reduction of antibiotic utilization for pediatric patients with ARTI, the proportion of adult ARTI patients receiving antibiotics in U.S. EDs is inappropriately high. Institution of measures to reduce inappropriate antibiotic use in the ED setting is warranted.