Hepatitis delta virus (HDV) was responsible for a high proportion of cases of acute and chronic liver disease in Southern Europe during the 1970s. Some data suggest that by the 1990s HDV circulation had substantially declined. We have assessed the prevalence of HDV infection and its clinical impact in 834 Italian hepatitis B surface antigen (HBsAg) carriers in 1997. Anti-HDV antibodies were sought in all consecutive chronic HBsAg carriers observed in 14 referral liver units throughout Italy. Risk factors for anti-HDV positivity were evaluated. Anti-HDV antibodies were found in 69 of 834 (8.3%) HBsAg-positive patients. Cohabitation with an anti-HDV-positive subject, intravenous drug addiction, residence in the South of the country, and the presence of cirrhosis were independently associated with the presence of anti-HDV antibodies. The overall prevalence of anti-HDV antibodies was lower than those observed in 2 multicenter surveys performed in 1987 and 1992 (23% and 14%, respectively). By 1997, the percentage of anti-HDV-positive subjects had sharply decreased in the 30 to 50 years age group, whereas it was almost unchanged in subjects over 50 years of age. The highest prevalence of anti-HDV antibodies (11.7%) was found in patients with cirrhosis. This prevalence was as high as 40% in the 1987 study. The circulation of HDV sharply decreased in Italy, by 1.5% per year, from 1987 to 1997. This decrease resulted mainly from the reduction in chronic HDV infections in the young, for whom high morbidity and mortality rates were recorded in the past. The results anticipate the almost complete control of HDV infection in the near future.