We report a 50-year-old female patient with a left-sided renal abscess caused by extended-spectrum β-lactamase-producing bacteria. According to the ORENUC classification she had phenotype N. The course was complicated by a perforation to an adjacent cyst and later to the renal pelvis. A primarily conservative approach of intravenous antibiotics had to be changed to an ultrasonography-guided percutaneous drainage of the lesion and insertion of a ureteral stent to stem a high volume of urine leakage. Drainage of a renal abscess is indicated if the size is larger than 3 cm according to EAU guidelines (relative size) or when the resolution does not occur after antibiotics. One-year follow-up showed the patient made a full recovery with no recurrence of a urinary tract infection or of any abscess.