Viral hepatitis type C is of public health importance in all parts of the world. In Italy, hepatitis C accounts for approximately 18% of the annually reported cases of acute viral hepatitis. The national rate of acute non-A, non-B hepatitis (the majority of which are hepatitis C) has significantly decreased during the last decades. At present, the onset of the disease occurs more frequently in individuals 15-24 years old, in men more frequently than in women and in persons living in the south of the country. During the last 5 years the rate of transfusion-associated hepatitis C has dropped (4.8 cases per 1,000,000 in 1989 versus 0.4 per 1,000,000 in 1993), while the percentage of patients who are intravenous drug abusers (IVDA) has increased from 18% to 33%. The high prevalence of anti-HCV (hepatitis C virus) antibody in blood and blood products recipients, IVDA and health-care workers with occupational exposure to blood indicates that HCV is efficiently transmitted parenterally. Data concerning transmission of HCV from mother to infant or by person-to-person contact, either by sexual or by non-sexual household contact, are controversial. However, there is almost universal agreement that the presence of concurrent infection with HCV and human immunodeficiency virus enhances the rate of vertical/perinatal HCV transmission as well as transmission through sexual and other types of person-to-person contact.(ABSTRACT TRUNCATED AT 250 WORDS)