Encephalopathy in a common neonatological sense is a term referring to a complex of clinical symptoms occurring in term infants in the first days of their life as a result of hypoxic-ischemic lesions. However, if we accept the encyclopedic definition of encephalopathy as a vast or multifocal brain lesions caused by a variety of factors, we may use the term to describe all patients with traumatic, hypoxic or toxic brain lesions, and therefore also newborns at different levels of maturity. Contrary to term newborns, in which case the hypoxic-ischemic encephalopathy are mostly intrauterine, for preterm infants there is a number of factors which destroy neural tissue postnatally The occurrence of those factors is often influenced by elements of essential intensive care. The article describes the most common biochemical disturbances and clinical causes.