Systemic cancer is the second most common cause of death in developed countries and metastatic brain tumour the most common tumour of the central nervous system (CNS). As the incidence of brain metastases appears to be rising, more accurate non-invasive imaging modalities for diagnosis, prognosis, prediction and follow-up of treatment are requisites for efficient patient management. Positron emission tomography (PET) imaging has the ability to evaluate different aspects of tumour microenvironment on the molecular and cellular level and impact the workup of patients with brain metastasis. This article reviews the current application of PET imaging in patients with metastatic brain disease.