The TREAT Asia (Therapeutics, Research, Education, and AIDS Training in Asia) Network is building capacity for Human Immunodeficiency Virus Type-1 (HIV-1) drug resistance testing in the region. The objective of the TREAT Asia Quality Assessment Scheme - designated TAQAS - is to standardize HIV-1 genotypic resistance testing (HIV genotyping) among laboratories to permit rigorous comparison of results from different clinics and testing centres. TAQAS has evaluated three panels of HIV-1-positive plasma from clinical material or low-passage, culture supernatant for up to 10 Asian laboratories. Laboratory participants used their standard protocols to perform HIV genotyping. Assessment was in comparison to a target genotype derived from all participants and the reference laboratory's result. Agreement between most participants at the edited nucleotide sequence level was high (>98%). Most participants performed to the reference laboratory standard in detection of drug resistance mutations (DRMs). However, there was variation in the detection of nucleotide mixtures (0-83%) and a significant correlation with the detection of DRMs (p<0.01). Interpretation of antiretroviral resistance showed approximately 70% agreement among participants when different interpretation systems were used but >90% agreement with a common interpretation system, within the Stanford University Drug Resistance Database. Using the principles of external quality assessment and a reference laboratory, TAQAS has demonstrated high quality HIV genotyping results from Asian laboratories.