Radiofrequency ablation (RFA), an effective, locally directed therapy for unresectable liver metastases, can improve the survival of patients. As a functional imaging approach, (18)F-fluorodeoxyglucose positron emission tomography ((18)F-FDG PET) or PET-computed tomography (PET-CT) may play a crucial role in the follow-up after RFA. Our objective was to evaluate the diagnostic accuracy of (18)F-FDG PET or PET-CT for the detection of residual tumor following RFA of liver metastases. Studies reporting the diagnostic value of (18)F-FDG PET or PET-CT for patients with residual tumor after RFA of liver metastases were identified. The methodological quality of these studies was systematically evaluated, and the overall sensitivity and specificity of these data sets are reported. Seven studies involving 155 patients were examined. When (18)F-FDG PET or PET-CT was performed within 2 days of RFA, the overall sensitivity and specificity were 79% [95% confidence interval (CI): 70-87%] and 84% (95% CI: 75-91%), respectively. When (18)F-FDG PET or PET-CT was performed 1 week after treatment, the pooled sensitivity and specificity were 48% (95% CI: 18-79%) and 94% (95% CI: 70-100%), respectively. Finally, when (18)F-FDG PET or PET-CT was performed 3 months after treatment, the pooled sensitivity and specificity were 52% (95% CI: 22-81%) and 94% (95% CI: 70-100%), respectively. Both (18)F-FDG PET and PET-CT are effective in detecting residual tumor following RFA of liver metastases. The ideal time to perform these imaging studies is within 2 days of RFA treatment.