OBJECTIVE: To assess the health care utilization and emergency department (ED) charges for septic arthritis. METHODS: We performed a retrospective cohort study of ED visits with septic arthritis as the primary diagnosis using the US Nationwide Emergency Department Sample data from 2009-2012. We examined ED charges, hospitalization, and associated time trends. Multivariable models were adjusted for demographics (age, sex, insurance status, residence, and household income), comorbidity, and hospital characteristics to assess factors associated with ED charges and hospitalization. RESULTS: Septic arthritis was responsible for 16,382 ED visits in 2012 in the US, which constituted 0.01% of all ED visits. The number of ED visits was stable from 2009-2012. Total ED charges were $34.6, $30.6, and $36.9 million in 2009, 2010, and 2012, respectively, and mean ED charges were $2,149, $1,866, and $2,257, respectively. The majority of the patients with an ED visit for septic arthritis were hospitalized: 82%, 83%, and 84% in 2009, 2010, and 2012, respectively. Metropolitan residence and western US location were associated with higher ED charges, and the highest income quartile, renal failure, or osteoarthritis were associated with lower ED charges. Female sex, metropolitan residence, metropolitan teaching hospital status, and medical comorbidity (diabetes mellitus, hyperlipidemia, hypertension, chronic obstructive pulmonary disease, coronary heart disease, gout, osteoarthritis, renal failure, and heart failure) were associated with a higher risk of hospitalization. CONCLUSION: Comorbidities were associated with a higher risk of hospitalization after an ED visit for septic arthritis, but not higher ED charges. No time trends in ED visit incidence, ED charges, or hospitalization rate for septic arthritis from 2009-2012 were noted.