At least 4 nucleos(t)ide analogs have been approved for the treatment of chronic hepatitis B: lamivudine, adefovir dipivoxil, entecavir, and telbivudine. The introduction of these drugs has radically changed the treatment of this disease. The advantages of these drugs are their oral administration, excellent tolerability and efficacy in all types of chronic hepatitis B (compensated and decompensated disease). The limitations are the need for prolonged treatments, which hampers adherence and can cause selection of HBV strains resistant to distinct drugs. The resistance rate differs for each of the drugs. Nucleotide analogs such as adefovir and tenofovir are useful in patients resistant to nucleoside analogs such as lamivudine, entecavir and telbivudine and vice versa. In cases of resistance to one of these drugs, combined treatment is advised.