Purpose: To analyze the clinical course and treatment outcomes of patients with iatrogenic arterioportal fistula (APF) caused by radiofrequency (RF) ablation of hepatocellular carcinoma (HCC). Materials and Methods: Among the 1,620 hepatocellular carcinoma patients treated by RF ablation between January 2012 and August 2017, 99 who developed APF after RF ablation were included in this retrospective study. Depending on the extent of portal vein enhancement on arterial phase images, APF was classified as massive or nonmassive. The patients’ clinical course was investigated and statistically evaluated by univariable and multivariable analyses. Results: Thrombocytopenia (odds ratio [OR] = 3.939; 95% confidence interval [CI], 1.141–13.598) was the only risk factor for developing massive APF. Eleven patients underwent embolotherapy (technical success rate, 90.9%) and no patients experienced serious adverse events within 30 days of the procedure. Patients with massive APF (66.7%) had a significantly higher chance of a Child-Pugh score increase than did the patients with nonmassive APF (13.6%) (P < .001). Massive APF had a significantly lower chance of natural regression than did nonmassive APF (P < .001). Child-Pugh B (OR = 17.739; 95% confidence interval, 2.361–133.279) and massive APF without treatment (OR = 11.061; 95% confidence interval, 1.257−97.341) were independent risk factors for liver failure that led to death of liver transplant within 1 year after RF ablation. Conclusions: Massive APF caused by RF ablation is mostly irreversible and significantly worsens patients’ outcomes, but may be effectively treated with embolotherapy.