PURPOSE: To evaluate post-ablation syndrome after radiofrequency thermal ablation of malignant hepatic tumors. MATERIALS AND METHODS: Forty-two patients with primary (n=29) or secondary (n=13) hepatic tumors under-went radiofrequency thermal ablation. A total of 65 nodules ranging in size from 1.1 to 5.0 (mean, 3.1) cm were treated percutaneously using a 50W RF generator with 15G expandable needle electrodes. We retrospec-tively evaluated the spectrum of post-ablation syndrome including pain, fever(> or =38 C degrees), nausea, vomiting, right shoulder pain, and chest discomfort according to frequency, intensity and duration, and the findings were cor-related with tumor location and number of ablations. We also evaluated changes in pre-/post-ablation serum aminotransferase(ALT/AST) and prothrombin time, and correlated these findings with the number of abla-tions. RESULTS: Post-ablation syndrome was noted in 29 of 42 patients (69.0%), and most symptoms improved with conservative treatment. The most important of these were abdominal pain (n=20, 47.6%), fever (n=8, 19.0%), and nausea (n=7, 16.7%), and four of 42 (9.5%) patients complained of severe pain. The abdominal pain lasted from 3 hours to 5.5 days (mean; 20.4 hours), the fever from 6 hours to 5 days (mean; 63.0 hours). and the nau-sea from 1 hour to 4 days (mean; 21.0 hours). Other symptoms were right shoulder pain (n=6, 14.3%), chest discomfort (n=3, 7.1%), and headache (n=3, 7.1%). Seventeen of 20 patients (85%) with abdominal pain had a subcapsular tumor of the liver. There was significant correlation between pain, location of the tumor, and number of ablations. After ablation, ALT/AST was elevated more than two-fold in 52.6%/73.7% of patients, respectively but there was no significant correlation with the number of ablation. CONCLUSION: Post-ablation syndrome is a frequent and tolerable post-procedural process after radiofrequency thermal ablation. The spectrum of this syndrome provides a useful guideline for the post-ablation management.