Purpose: Focal metastasis may be treated with radiofrequency ablation (RFA), a low invasive method yet limited by the lack of direct evidence of radicality of treatment. We, hereby, aimed at assessing the role of positron emission tomography-computed tomography (PET/CT) with fluoride radiolabeled deoxy-glucose ([18F]FDG) in RFA treatment success evaluation and early diagnosis of local relapse of liver metastasis after RFA procedure. Methods: RFA was performed in nine patients on 12 liver metastasis, serially imaged through [18F]FDG-PET/CT and multidetector CT (MDCT) at 1, 3, 6, and 9 months after treatment. Eight lesions were also scanned with [ 18F]FDG-PET/CT at 1 week after treatment. Imaging analyses were performed on 47 [18F]FDG-PET/CT and 51 MDCT. Imaging reading outcomes were compared to each other and to biopsy tissue results when available. Results: In one case, [18F]FDG-PET/CT revealed radiotracer uptake at RFA site a week after procedure. Negative concordant outcome was obtained on eight lesions at 1 month after RFA, on eight cases at 3 months, on four at 6 months, and on two cases at 9 months. Extra-liver (peritoneal) disease was detected in one case by both [18F]FDG-PET/CT and MDCT. In seven cases, [18F]FDG-PET/CT revealed the presence of local recurrence earlier than MDCT. In no cases did MDCT detect local relapse earlier than [ 18F]FDG-PET/CT. Conclusion: [18F]FDG-PET/CT may detect RFA treatment failure as well as local relapse after RFA earlier than MDCT. © 2008 Springer-Verlag.