The Japanese diagnostic guidelines for autoimmune hepatitis (AIH) were proposed in 2014. This study aimed to determine the trends and characteristics of AIH based on a Japanese nationwide survey. Data for 796 patients who were newly diagnosed with AIH from 2014 to 2017 were collected from January to March, 2019 from 54 hospitals throughout Japan. Clinical characteristics, including treatment, were compared with those reported in a prior 2015 survey. The population had a median age of 63 years at diagnosis, and the male to female ratio was 1:5.3. The numbers of women was significantly lower in this survey than in the 2015 survey. Moreover, the incidence of AIH with histological acute hepatitis increased significantly from 11.0 to 21.7%. The changes in the laboratory findings, such as in transaminase and immunoglobulin G levels and antinuclear antibody titers, as well as in prednisolone treatment, reflected an increasing incidence of acute AIH. The clinical characteristics of AIH changed rapidly, in parallel with the increasing incidence of acute AIH. The elucidation and diagnosis of AIH with acute hepatitis are important in the management of AIH. Although autoimmune hepatitis (AIH) with an acute presentation is difficult to diagnose based on a scoring system because of low immunoglobulin G (IgG) levels and antinuclear antibody (ANA) titers, its clinical and histological characteristics have been gradually elucidated by several reports 1-18. AIH with an acute presentation includes two types: (1) the acute exacerbation phase, in which patients present with the clinical features of acute hepatitis, with histological evidence of chronic hepatitis; and (2) the acute hepatitis phase, in which patients present with histological features of acute hepatitis 11. Regular nationwide surveys of AIH have been conducted since 1975 in Japan 1,2,19-21. The 2015 survey reported the trends in 1682 patients who were diagnosed with AIH from 2009 to 2013 2. The proportion of AIH cases with acute hepatitis (11.