The subjects of this paper are mainly the encephalitis of viral origin and in addition 3 types of non-viral encephalitis of practical importance. A review is given on the current diagnostic possibilities including clinical criteria examination of the cerebrospinal fluid neuroradiology and etiological investigation by means of direct identification of the microbes in the cerebrospinal fluid or by measuring intrathecally produced antibodies. After some general statements concerning treatment the specifically treatable encephalitis caused by Herpes simplex virus, Mycoplasma pneumoniae, Borrelia burgdorferi and Toxoplasma gondii are discussed in more detail.