Background/Aim. Acute non-A, non-B, non-C, non-D, non-E hepatitis (non-A-E AH) is an acute disease of the liver of unknown etiology for which one or more new, so far undetected, hepatotropic viruses may be responsible. The frequency of non-A-E AH ranges from 3.8% to 33.9%, and therefore it has a significant place within current infectology and hepatology. The aim of our study was to establish the frequency, clinical and biochemical characteristics, natural course and outcome of non-A-E AH and compare them with control groups affected by acute viral hepatitis A, B and C. Methods. This descriptive-analytic prospective study included 31 patients with non-A-E AH treated at the Institute of Infectious and Tropical Diseases, Clinical Center of Serbia, Belgrade, from 2003 to 2008. They were followed up during the period not less than 6 months. The controls involved randomly selected patients, treated at the same time with a definite diagnosis of acute viral hepatitis A, B and C. Statistical data analysis used Mann-Whitney Utest, Student's t-test and variance analysis. The value of p < 0.05 was considered statistically significant. Results. The frequency of non-A-E AH was 7.6%. Almost no difference was found between sexes (male/female ratio was 1 : 1.07); it was developed in all age groups, with the highest incidence in the middle age (mean age was 38.32 ± 15.3 years). It appeared equally throughout the whole year. Out of risk factors, inoculation risk was predominant (before all, dental interventions), mostly involving urban population living in comfortable conditions. The duration of incubation varied much ranging from 20 to 180 days (median 60 days). By clinical course, moderate and icteric forms were most common, mostly corresponding to acute hepatitis A and C. On the other hand, by duration of the disease (mean duration was 67.1 ± 27.1) and chronic transformation, non-A-E AH resembled to acute hepatitis B. Progression to chronicity was recorded in 9.68% of the patients. There was no fulminant neither cholestatic form of the disease. Conclusion. Based on the results obtained in this study, it is probable that there are some so far undetected primary hepatotropic viruses in our environment.