Several reports show that presence or absence of extrahepatic disease is a determining prognostic factor. Patients with extrahepatic disease are rarely suited for resection of the liver metastases. Recently several papers describe that the proliferation index of the liver metastases is another determining prognostic factor. Patients with a high proliferation factor have a worse prognosis. For both of these determining factors, it seems that PET diagnostics play an essential role and contribute to better selection of patients suitable for resection.