['Neuropsychiatric toxicity is a common dose-limiting side effect of interferon therapy. The primary aim of this study was to determine whether patients receiving long-term low-dose peginterferon therapy had a higher incidence of cognitive side effects compared with untreated patients enrolled in the Hepatitis C Antiviral Long-Term treatment against Cirrhosis (HALT-C) Trial.', 'A total of 129 patients with chronic hepatitis C and advanced fibrosis completed a battery of 10 neuropsychological tests and the Beck Depression Inventory at pretreatment baseline and at months 12, 24, 36, and 48 while receiving long-term peginterferonalpha2a (90 microg/week) or no therapy during the randomized phase of the HALT-C Trial. Cognitive impairment was defined as a global deficit score (GDS) > or = 1.0.', 'The mean age was 51.2 years, 67% were male, and 42% had cirrhosis. After accounting for baseline GDS scores, the mean GDS scores did not significantly change over time (P=0.46) nor with treatment group (P=0.49). Cognitive function was also not influenced by medication adherence in the 66 patients receiving maintenance peginterferon (P=0.14) after controlling for baseline GDS scores and time. Beck Depression scores did not significantly increase over time (P=0.60), nor did they vary by treatment group (P=0.74). Although 32% of patients experienced objective worsening of their liver disease during follow-up, the frequency and severity of cognitive impairment did not differ in those with and without disease progression (P=0.71).'] Does cognitive function worsen during long-term low-dose peginterferon therapy in patients with chronic hepatitis C?