Injection drug users (IDUs) have the highest hepatitis C (HCV) infection rates of any risk group in the United States; fully 70-96 percent of IDUs have been infected. Natural history studies of transfusion recipients have suggested that HCV infection represents a slowly progressive disease culminating in cirrhosis and liver cancer after decades. But while active IDUs represent the largest single group of persons infected with HCV, there are no studies to date describing the prevalence and severity of HCV-related liver disease among street-recruited, actively injecting IDUs. Because most IDUs acquired HCV when they began injecting decades ago, many are at imminent risk for life-threatening complications. We propose a cross-sectional study of 1000 active, street-recruited IDUs who test positive for HCV antibody in the Urban Health Study's ongoing program of HIV and hepatitis testing in inner-city neighborhoods in San Francisco. In-depth epidemiological, clinical and laboratory evaluations of HCV-positive participants will be conducted to assess signs, symptoms, and correlates of liver disease. A subset of 200 HCV-positive participants will undergo liver biopsies. Specifically, this study aims to: 1) to describe the clinical and laboratory spectrum of HCV-related liver disease among 1000 active, street-recruited IDUs in San Francisco, 2) to determine the correlates of advanced liver disease among active IDUs, including demographic factors, injection and other behaviors, comorbidities, and viral markers. Advanced liver disease will be defined as Child-Pugh score B or greater, 3) to describe the histologic spectrum of HCV-related liver disease in a subset of 200 active IDUs who will undergo liver biopsy, and 4) to determine the correlates of progressive liver disease among the 200 IDUs who undergo biopsy. Progressive liver disease will be defined as fibrosis stage 3 or 4 on liver biopsy. In addition, contact information will be collected so that this cross-sectional study can serve as a baseline for future cohorts to examine the incidence of clinical and histological disease in this cohort.