The introduction of HBV vaccination in Italy has led to a decline in new HBV infections. Increasing immigration over recent years suggests a change in short-term epidemiology of HBV. The aim of this study was to assess the prevalence of HBV infection in the general population living in the catchment area of Legnano Hospital (Northern Italy). In the period 2007-2008, 22,758 inpatients and outpatients were examined for Hepatitis B surface antigen (HBsAg), of whom 1,654 (7.3%) were of foreign origin. Of the 488 patients who were positive for HBsAg (2.1%), 381 (1.8%) were Italian and 107 (6.5%) were born in other countries. In terms of age, the prevalence of HBsAg was significantly higher among non- Italians in every age group (other than those aged >60 and <11 years), and in many of the selected subgroups: the inpatients of some departments (35.4% vs 17.2%), pregnant women (5.3% vs 0.3%), blood donors (4.7% vs 0.1%), and hospital staff (6.4% vs 1.3%). Non- Italians were affected by 16.7% of acute infections and 24.3% of chronic infections; they also accounted for 42.6% of subjects with carrier state, 16.0% of patients with chronic hepatitis, and 12.2% of patients with cirrhosis. In our area, the overall prevalence of HBsAg among Italians is less than 2% (as expected following the introduction of HBV vaccination), but it is significantly higher among patients from areas highly endemic for HBV infection who represent a new reservoir for HBV infection.