In the recent scale-up of antiretroviral treatment, gender differences in access to treatment have been reported. In Thailand, as the HIV epidemic became more generalised, there has been a shift from men being disproportionately affected to increased vulnerability of women. In 2007, the Living with Antiretrovirals (LIWA-ANRS 12141) study investigated the gender distribution of all adult patients receiving antiretroviral therapy (N=513 patients) in four community hospitals in northern Thailand and factors influencing the disparities observed. From this retrospective life-event history survey, we found that proportionately more women (53%) were receiving antiretroviral therapy than men, an unexpected result for a country with a higher proportion of infections among men. They were more likely to initiate treatment within one year of diagnosis and were at a more advanced stage of the disease compared to women. This gender distribution is partly explained by the evolving dynamics of the HIV epidemic, initial prioritization of mothers for treatment and earlier access to HIV testing for women. These issues are also entangled with gender differences in the reasons and timing to HIV testing at the individual level. This study found that the majority of men underwent HIV testing for health reasons while the majority of women were tested following family events such as a spouse/child death or during pregnancy. Further qualitative research on gender specific barriers to HIV testing and care, such as perceived low risk of infection, poor access to medical care, lack of social support, actual or anticipated HIV/AIDS-related stigma would provide greater insight. In the meantime, urgent efforts are needed to increase access to voluntary counselling and testing inside and outside the family setting with targeted interventions for men.