Expression of hepatitis delta virus (HDV) markers was investigated in sera from 310 patients with acute hepatitis, 63 chronic hepatitis B surface antigen (HBsAg) carriers and 76 drug addicts positive for at least one serological hepatitis B virus (HBV) marker. Acute HDV infection occurred in 17.1% of the patients with acute hepatitis. Among 40 cases of coinfection, hepatitis was severe in ten and fulminant in three. Only two of the 13 superinfected patients showed a severe hepatitis, but a high percentage (78%) of them developed chronic hepatitis one year after HDV infection. Also in our area parenteral drug addiction represents the main factor of risk for HDV infection. The high prevalence of HDV infection in our area points to the necessity for serological screening for HDV markers in patients with acute and chronic hepatitis.