Many issues regarding the epidemiology of hepatitis C infection require further investigation. These include determining the prevalence of hepatitis C in populations that are at a greater risk for infection given the high prevalence of HIV/AIDS associated with injection drug use; exploring the role of sex-related practices in transmission; and assessing the role of other potential risk factors in infection. The proposed study examines seroprevalence of hepatitis C infection and assesses sex-related practices, other risk behaviors, and patterns of co-infections that might promote transmission among the household population aged 18 to 64 years in Puerto Rico. To our knowledge, this is the first population-based study to estimate the prevalence of hepatitis C infection and investigate correlates of infection in a homogeneous population of Hispanic origin. Findings from this study can contribute to understand the burden of this infection in a Hispanic population and provide baseline data for comparison purposes with other mainland Hispanic groups that will ultimately lead to interventions that may reduce the risk of transmission of hepatitis C virus. The specific aims of the study are: 1. To estimate the seroprevalence of hepatitis C infection for the household, adult population and for specific population groups defined by age, sex, and geographic stratification regions 2. To assess the role of specific sex-related practices in hepatitis C infection, controlling for injection drug use and socio-demographic characteristics 3. To examine the role of other potential risk factors (body piercing, tattooing, non-injecting drug use, and shared use of drug paraphernalia) in hepatitis C infection, controlling for socio-demographic characteristics 4. To assess the patterns of hepatitis C co-infections with hepatitis B, HIV and herpes simplex 5. To assess the relationships between high-risk behaviors (drug use practices and sex-related practices) and hepatitis C co-infections with hepatitis B, HIV and herpes simplex The study design is based on a multistage, household probability sample of 2,000 adults selected throughout the island. Previous investigations have shown that Puerto Rican drug users have higher levels of risk behaviors than their counterparts in the U.S. mainland. Therefore, a larger prevalence of hepatitis C infection is expected in the island, with marked variations in the magnitude of the risk attributable to injection drug use, sex-related practices, and non-injection sources.