Summary. Switching to adefovir (ADV) monotherapy is effective in patients with lamivudine (LAM)-resistant hepatitis B virus (HBV) mutations (rtM204 I/V). However, it was recommended to continue LAM therapy for months after starting ADV therapy for safety concern. The safety and efficacy of switching to ADV monotherapy was examined in compensated and decompensated patients with liver cirrhosis. The clinical, biochemical and virological responses were compared between ADV monotherapy in 18 cirrhotic patients and ADV add-on LAM therapy in 10 comparable cirrhotic patients with LAM-resistant rtM204 I/V. After switching to ADV monotherapy, Child-Pugh's score, serum alanine aminotransferase (ALT), bilirubin, albumin and HBV DNA levels improved significantly (P < 0.01). Serum HBV DNA response, defined as HBV DNA decreased to below 105 copies/mL or ≥2 log10 reduction form baseline, was achieved in all patients. A transient ALT flare without concurrent changes in serum bilirubin or prothrombin time was observed in only two patients (11%). The efficacy and safety profile was similar to those with ADV add-on LAM therapy. In conclusion, switching to ADV monotherapy after emergence of LAM-resistant rtM204 I/V is effective and safe in cirrhotic patients, even in those with hepatic decompensation. To stop LAM and switch to ADV in patients with breakthrough is a reasonably safe and cost-effective approach.