The prognosis for patients with decompensated hepatitis B virus (HBV) related liver cirrhosis (LC-B), especially for those with LC-B complicated with hepatocellular carcinoma (HCC), is poor. We investigated the effects of lamivudine in patients with decompensated LC-B, with and without HCC. Decompensated LC-B patients (n=55) with Child-Pugh classification scores (CPS) >7 points were enrolled. All were admitted to the hospitals of the authors between January 1997 and December 2004. Decompensated cases due to a severe exacerbation of hepatitis with CH-B and patients with HCC showing an extra hepatic metastasis or portal vein tumor thrombus were excluded. Some 19 cases (including 5 cases complicated with HCC at the start of therapy) were treated with lamivudine at 100 mg/day (L group), and 36 (including 7 cases with HCC at time of admittance) were treated without lamivudine (non-L group). The median of CPS points in the L group was higher than that of non-L group (11 points versus 9 points, p<0.02). Prothrombin time (%), albumin, ascites, CPS, and HBV-DNA quantity were each significantly improved after 6 months in the L group (p<0.05). A mutation in the YMDD motif was observed in 5 patients in the L group, however liver function did not deteriorate. Further, the survival rate was significantly higher in the L group (p<0.05). HCC was found in 3 L group and 4 non-L group patients during the study. In the L group, all patients complicated with HCC were treated repeatedly or until cured, whereas 91% of those in the non-L group could not be treated (p<0.01). Our results suggest that lamivudine is a useful and important therapy for patients with decompensated LC-B with and without HCC, as well as those who are restricted from having liver transplantation.