Aim The rising HIV infection rates among women especially of child bearing age particularly in Sub-Saharan Africa expose children to increased HIV risk even before they are born. Without effective measures or awareness campaigns to deal with mother-to-child transmission, 390 000 out of the global 430 000 children newly infected with HIV during 2008 were from sub-Saharan Africa. This study was undertaken to assess HIV/AIDS related knowledge, attitude and risk perception among pregnant women in Tertiary hospital, Southwestern Nigeria. Method The study was carried out using a 43- item self administered questionnaire, pretestd and administered to 403 pregnant women during ante-natal clinic sessions. Results High HIV/AIDS awareness level (97%) was recorded, 77.7% had correct knowledge of the cause of the disease but knowledge on the modes of vertical transmission during pregnancy (57.5%) and prevention during breast-feeding (62.3%) was not encouraging. A lot of misconceptions about the cause of the HIV/AIDS, modes of contact, transmission, prevention and anti-retroviral therapy were recorded. Conclusion The survey revealed that a lot needed to be done to improve the knowledge, attitude, perception and behavioral changes among the populace especially in this particular group. This calls for urgent and proper response in order to stem the tide of HIV/AIDS.