Since 2000, the International AIDS Society-USA (IAS-USA) Drug Resistance Mutations Group has worked as an independent entity and forged a collaborative process to identify key HIV-1 drug resistance mutations. The goal of the group is to quickly deliver accurate and unbiased information to clinical practitioners on HIV-1 resistance. This April 2005 version of the IAS-USA Drug Resistance Mutations Figures replaces the version published in this journal in October 2004. The IAS-USA Drug Resistance Mutations Figures are designed for use in identifying mutations associated with viral resistance to antiretroviral drugs and in making therapeutic decisions. Care should be taken when using this list of mutations for surveillance or epidemilogic studies of transmission of drug-resistant virus. A number of amino acid substitutions, particularly minor mutations, represent polymorphisms that, in isolation, may not reflect prior drug selective pressure or reduced drug susceptibility.