In a randomized, controlled trial that demonstrated the efficacy of interferon alfa-2b 3 million units three times a week for 24 weeks in controlling chronic hepatitic C (non-A, non-B), the Sickness Impact Profile (SIP) was used to evaluate the impact of disease and treatment on health-related quality of life (HRQOL). The SIP was self-administered by 160 patients before treatment, at the end of treatment, and at the study endpoint. Before treatment, patients with chronic hepatitis C scored significantly (P < 0.05) higher (worse) than an historical control group of the general population in mean total SIP score and in all categories except eating. The highest degree of impairment was observed in the work, sleep and rest, and recreation and pastimes categories. After treatment, patients who received interferon alfa-2b had significant (P < or = 0.05) improvement in work, sleep and rest, and recreation and pastimes scores. Numerical improvement was observed in total score, physical and psychosocial dimension scores, and most individual category scores. Mean SIP scores were unchanged or slightly worsened in untreated control patients. In responders (patients with improvement in serum alanine aminotransferase levels), the largest improvement was seen in work scores. The SIP appears to be a reliable and valid instrument for describing the impact of chronic hepatitis C on HRQOL but lacks disease-specificity and the ability to reflect clinically relevant changes. Thus the SIP is not the best instrument to evaluate the HRQOL effects of treatment with interferon alfa-2b in patients with chronic hepatitis C.