OBJECTIVES: The aim of this study was to determine the risk factors and clinical characteristics of community-acquired acute pyelonephritis (CA-APN) caused by extended-spectrum ß-lactamase (ESBL)-producing organisms. METHODS: From March 2010 to February 2011, patients with CA-APN were recruited in 11 hospitals in South Korea. Clinical and microbiological data were collected prospectively, and the ESBLs and multilocus sequence types of the ESBL-producing Escherichia coli were characterized. Comparison between CA-APN caused by ESBL-producing Enterobacteriaceae and those by non-ESBL-producing organisms was performed. RESULTS: A total of 566 patients were recruited. Enterobacteriaceae were detected in 526 patients. Forty-six isolates (46/526, 8.7 %) were positive for ESBLs. Clinical and microbiological failure did not differ between the two groups, despite there being fewer patients with ESBL-positive isolates provided with appropriate antibiotics initially (19.6 vs. 93.8 %, p < 0.001). However, the duration of hospitalization was longer in the ESBL group (10.5 vs. 7.0 days, p = 0.012). In a logistic regression model, Charlson score ≥1 point [odds ratio (OR) 3.4, 95 % confidence interval (CI) 1.6-7.0, p = 0.001], antibiotics usage during the previous year (OR 3.1, 95 % CI 1.4-7.2, p = 0.008), and urinary catheterization during the previous month (OR 4.4, 95 % CI 1.1-17.6, p = 0.035) were associated with the risks of CA-APN by ESBL producers. CTX-M-15 (48 %) and CTX-M-14 (38 %) were the most common ESBLs. ST131 was the most common clone (7/24, 29.1 %), which was more frequently resistant to cefepime, fosfomycin, and temocillin. CONCLUSIONS: The risk factors for CA-APN by ESBL producers were Charlson score ≥1 point, antibiotics usage during the previous year, and urinary catheterization during the previous month.