Neuroinflammation is a complex biological response to any injury occurring to the central nervous system. It is mainly characterized by the recruitment of immune system cells, namely the microglial cells, in the site of injury. Once activated, microglia expresses a cholesterol transporter protein (TSPO), previously also known as peripheral type benzodiazepine receptor. PK11195 is a ligand for TSPO and, labelled with a positron emitter, it is also the most used tracer for PET molecular imaging to in vivo map the microglia activation in various neurological disorders, including ischemic stroke. Recent [(11)C]PK11195 PET studies proved activated microglia both locally in the area of the infarct and at distance along the affected fibre tracts, suggesting the presence of two different microglia subtypes with peculiar functions in disease progression. The aim of this review is to discuss the most recent knowledge about imaging neuroinflammation in ischemic stroke and in the atherosclerotic and vascular inflammatory disorders, trying to elucidate the interplay between the clinical course and the activation of a microglial response.