Acute hepatitis D, one of the clinical diagnoses of viral hepatitis D, is defined as HDV/HBV co-infection. The incubation period is 4 to 20 weeks. Clinical manifestations and biochemical features are similar to those of simple acute hepatitis B. There may be malaise, lack of appetite, jaundice and hepatomegaly. What are the manifestations and how to diagnose intrahepatic HDAg with only transient positivity? The possibility of simultaneous or overlapping HDV infection should be considered in patients with hepatitis B, HBsAg carriers with marked fluctuations or progressive deterioration, and in patients with severe hepatitis, and confirmation of diagnosis depends on laboratory tests. 1, acute HDV/HBV co-infection: patients with acute hepatitis, in addition to positive markers of acute HBV infection, positive serum anti-HDIgM, positive anti-HDIgG low titer; or positive serum and/or intrahepatic HDAg, HDV-RNA. 2. HDV/HBV overlap infection: chronic hepatitis B patients or chronic HBsAg carriers with positive serum HDV-RNA and/or HDAg; or high titers of anti-HDIgM and anti-HDIgG; or positive intrahepatic HDV-RNA and/or HDAg. Some patients have two transaminase peaks. Because of the short duration of acute hepatitis B HBVemia, HDV infection is often terminated with the disappearance of HBV, so intrahepatic HDAg is only transiently positive, and serum anti-HDIgM is transiently elevated in low titers, followed by secondary anti-HDIgG. The risk of developing chronic hepatitis is no higher than that of HBV infection alone.