Every minute, five people under 25 are infected with HIV. One in three persons living with HIV/AIDS is age 15-24 and most of them are unaware that they carry the virus. Millions more have little or no knowledge of the disease and do not know how to protect themselves or take measures to prevent the spread of the disease. The aim of this paper was to assess the comprehensive knowledge of HIV/AIDS among young married Scheduled Castes women in Thiruvarur district, Tamil Nadu. Multistage stratified random sampling technique was applied to select 605 women in the age group of 15-24 years in all the five blocks in the period of ten months from July 2010 to April 2011. Result reveals that 91% of women had knowledge about the HIV/AIDS. Around 61.5% had high comprehensive knowledge of HIV/AIDS prevention and transmission among the respondents. The age of women, education of women, standard of living index and exposure to mass media had statistically significant association with comprehensive knowledge of HIV/AIDS. The women who were more exposed to mass media were more likely to get knowledge of HIV/AIDS than the less exposed women (OR= 1.977). It concludes that health awareness program should be launched to enhance their knowledge of sexual health problems in the study area.