Acute encephalitis is one of the most common central nervous inflamatory diseases,specially in children,cause by viruses and others etiologies with hight mortality and sequale. Airm of the study: to describe etiology, clinical and laboratories feature by the causes of the disease. During one years, from July 2012 to June 2013 there were 520 patients suffered from Acute Encephalitis admitted in National Hospital of Pediatrics. The Etiologies were founded in 239 patients (46 percent).The leading cause were viruses (94,5 percent),including JE 41,8 percent, HSV 24,3 percent, EV 17,6 percent...Mean age of JE and EV patients was 6-7 years, HSV was 1-2 years. old. The number of disease increased in the summer. Clinical characteristics by the causes: General convulsion was most frequent in JE (75 percent), Local convulsion and paralysis were typical for HSV (81 percent and 56 percent). Brain MRI showed that the local inflammatory at temporal lobe was frequent for HSV, thalamus lesion was frequent for JE. Conclusion: The Etiologies of Acute Encephalitis in children were found in 46 percent of all cases (much higher than previous time). The leading causes still remained as JEV, HSV and EV, the less were bacterias, fugal and parasites. There are some differences in epidemiology, clinics and paraclinnics by the cause were noticed.