Purpose To perform a single-center study of contrast material-enhanced ultrasonography (US)-assisted percutaneous nephrostomy (PCN) for patients with nondilated renal collecting system. Materials and Methods An international review board approved this retrospective study with waiver of informed consent for participation, and the study was approved by the Ethical Committee. From November 2011 to September 2015, 47 patients (mean age, 51.9 years ± 16.2 [standard deviation]; range, 18-80 years) with clinical necessity of urinary drainage, urinary diversion, or provision of access to the collecting system and with nondilated renal collecting system who underwent contrast-enhanced US-assisted PCN for 48 kidneys were included. US contrast agent was injected through the puncture needle and the drainage catheter to confirm successful PCN. The technical success rate and complications were evaluated. Relative frequencies with 95% confidence intervals (CIs) were calculated. Results The technical success rate was 100% (47 of 47, 95% CI: 93.8%, 100%) per patient and 100% (48 of 48, 95% CI: 94.0%, 100%) per kidney. For each kidney, the mean number of needle passes was 1.4 ± 0.5 (range, 1-3). The mean duration of the complete procedure was 18.9 minutes ± 4.8 (range, 8-30 minutes). The mean dose of contrast agent was 12.9 mL ± 3.2 (range, 8-25 mL). No major complications were observed. After a follow-up of 1-30 days (mean, 18.4 days ± 10.3), only four patients (four of 47, 8.5%, 95% CI: 2.37%, 20.4%) had minor complications, including one perirenal hematoma seen at US 9 days after the procedure and three patients with transient macroscopic hematuria that lasted 1-2 days. Conclusion Contrast-enhanced US-assisted PCN in patients with nondilated renal collecting system is valuable with high technical success rate. RSNA, 2017.