Hepatitis C is the most common cause of chronic liver disease in the United States and it significantly reduces quality of life. The role of cognitive deficits contributing to the morbidity of this disease has not been well characterized. The purpose of this study was to examine cognitive functioning in patients with chronic hepatitis C and to investigate relationships among parameters of disease severity and performance on neuropsychological tests. Sixty-six patients with chronic hepatitis C and 14 patients with other chronic liver diseases were administered a brief battery of neuropsychological tests assessing attention, visuoconstructional ability, learning, memory, and psychomotor speed. Cognitive impairment in patients with chronic hepatitis C ranged from 0% on a visuoconstructional task to 82% on a measure of sustained attention and concentration. Test scores of patients with chronic hepatitis C did not differ from those of patients with other chronic liver diseases. Hence, patients with and without chronic hepatitis C experience cognitive deficits, especially in tasks requiring attention and psychomotor speed. In addition, there was a significant relationship between fibrosis stage and test performance, with greater fibrosis associated with poorer performance. However, both patients with and without cirrhosis exhibited cognitive dysfunction. In conclusion, these findings suggest that progressive hepatic injury may result in cognitive problems even before the development of cirrhosis. Future studies need to determine the effect of this decrease in cognitive function on quality of life.