We carried out a multicentre study on 2830 patients with chronic liver disease from 79 liver units (25 in northern, 24 in central and 30 in southern Italy) to evaluate naturally acquired immunity against hepatitis A virus (HAV) in relation to age, sex, geographical area of origin and entity of liver disease, and to define the strategy for specific vaccination. Antibody to HAV (anti-HAV) was detected in 1514 (53.5%) of the 2830 patients tested; the prevalence was 50.4% in males and 59.1% in females. Both in central and southern Italy the prevalence of anti-HAV positive subjects increased with increasing age from 43.3 and 44.7%, respectively, in the 0-30-year-old subjects to 80.1 and 68.3%, respectively, in those aged over 60 years. The overall prevalence was much lower in northern Italy, as were the variations from one age group to another, from 28.4% in the 0-30-year-old subjects to 38% in those aged over 60 years. 40.6% of patients with cirrhosis lacked naturally acquired protection against HAV; this percentage was higher in northern (60.5%) than in central (34.9%, P < 0.0001) and southern Italy (27.6%, P < 0.0001). The high prevalence of patients in Italy with chronic hepatitis or cirrhosis who lack naturally acquired immunity to HAV warrants the implementation of vaccination programmes against hepatitis A in such patients.