Minimal hepatic encephalopathy (MHE) has a negative effect on patients' daily functioning. Thus far, no study has investigated the effect of treatment-related improvement in cognitive functions on health-related quality of life (HRQOL). We measured psychometric performance by number and figure connection tests parts A and B, picture completion, and block design tests and HRQOL by the Sickness Impact Profile (SIP) of 90 patients with cirrhosis on inclusion into the study and 3 months later. A Z score less than -2 on the neuropsychological (NP) tests was considered abnormal. Sixty-one (67.7%) patients had MHE. They were randomly assigned in a 1:1 ratio to receive treatment (lactulose) for 3 months (n=31) or no treatment (n=30) in a nonblinded design. The mean number of abnormal NP tests decreased significantly in patients in the treated group (baseline, 2.74 [95% CI 2.40-3.08]; after 3 months, .75 [95% CI .36-1.16]) compared with patients in the untreated group (baseline, 2.47 [95% CI 2.19-2.74]; after 3 months, 2.55 [95% CI 2.16-2.94]); multivariate analysis of variance (MANOVA) for time and treatment, P=0.001. The mean total SIP score improved among patients in the treated group (baseline, 10.39 [95% CI 9.36-11.43]; after 3 months, 3.77 [95% CI 2.52-5.02]) compared with patients in the untreated group (baseline, 10.36 [95% CI 8.98-11.73]; after 3 months, 10.39 [95% CI 8.36-12.42]); MANOVA for time and treatment, P=0.002. Improvement in HRQOL was related to the improvement in psychometry. CONCLUSION: Treatment with lactulose improves both cognitive function and HRQOL in patients with cirrhosis who have MHE.