Introduction. The blood-brain barrier (BBB) constitutes a well-defined structure which plays a role in the normal homeostasis of the central nervous system (CNS) and in certain disease processes affecting it. Methods. Over 50 reviews and peer-reviewed experimental publications published over the last few years that discussed development, normal morphology and function of the BBB, function defects and its role in the development of CNS pathology were reviewed. The mechanisms determining BBB functional impairment and their effect upon CNS pathology are discussed. Results. The BBB role as a physic and metabolic barrier is to isolate the CNS from the rest of the organism. However, the BBB does not behave as a passive structure. It plays an active role in the maintenance of the normal function of the CNS. Depending on the presence of injury or some systemic signals, the integrity of the BBB can be compromised, increasing its permeability. Conclusions. The morphological and functional characteristics of the BBB are key for certain CNS diseases. It also limits their therapeutic approaches. The possibility to modify the BBB permeability in a controlled way, with spatial and temporal restrictions, potentially could change both prevention and treatment for several diseases of the CNS