The aim of the study was the evaluation of the detectability of treated liver metastases using one FDG-PET measurement. The study includes 42 patients (80 lesions) from different primary tumours. Standardized Uptake Values (SUV) as well as the tumour to liver Ratio (T/L) were used for evaluation. A T/L > 1.0 was considered to be pathological. Clinical follow-up data for at least 6 months were used as a reference. The median value of the FDG-uptake was 2.9 SUV in all liver metastases. The sensitivity based on a T/L ratio exceeding 1.0 was 82.5% (66/80 lesions). 25 of 80 (31%) lesions had a ratio T/L higher than 2.0 and were clearly visualized by PET. Negative results with a ratio T/L < 1.0 were raised in 14 of 80 treated metastatic lesions (17.5%). Although these metastases were hypometabolic, they were correctly classified due to the image correlation with computed tomography (CT) or magnetic resonance (MR) images or due to a baseline FDG-study prior to the onset of therapy. False positive results were not noted in this study. FDG-PET is a reliable method for the evaluation of treated liver metastases. A baseline FDG study prior to therapy is preferable for the interpretation.