The aim of this study was to assess the factors associated with the deci- sion to have HIV antibody testing among Thai men who have sex with men (MSM) during the previous 12 months. MSM were recruited by systematic sampling from the M-REACH membership registry. Variables collected were demographics, sexual behavior, health behavior, knowledge about HIV/AIDS prevention and attitudes about HIV antibody testing. Data were collected via a self-administered questionnaire and in-depth interviews. About one third of participants reported having HIV antibody testing during the previous 12 months. Of those, 65% were aged > 24 years. Participants aged > 24 years were significantly more likely to have HIV testing than those aged < 24 years (AOR = 3.04, 95% CI: 1.12-8.28; p < 0.005). Most participants exhibited a good knowledge and attitude (levels regarding HIV antibody testing and AIDS). Those with a good attitude level about HIV were more likely to have been tested than those with a poor attitude level (AOR = 3.19; 95% CI: 1.24-8.22; p < 0.005). A programs that improves attitude and knowledge levels about HIV testing need to be developed for MSM in Thailand to improve HIV antibody testing rates.