Over the period 1989-1991 a case-control study was carried out in the area of Naples comparing 162 subjects with acute hepatitis B and 788 hospitalized control subjects. The results of multivariate analysis showed that surgical intervention (odds ratio 3.8; 95% CI 1.2-11.7), household contact with an hepatitis B surface antigen (HBsAg) positive carrier (odds ratio 2.7; 95% CI 1.1-6.7) and intravenous drug use (odds ratio 13.0; 95% CI 3.2-52.7) were risk factors independently associated with hepatitis B. No association was found with the other risk factors considered, such as blood transfusion, hospitalization, other percutaneous exposures, dental therapy, contact with an icteric case, barber shop shaving and two or more sexual partners. As a significant proportion of the general population undergoes surgical intervention, efficient procedures for sterilization of instruments should be implemented, together with the use of disposable materials, to control the spread of HBV infection in surgical settings.