Background: Sub-Saharan Africa remains the region most heavily affected by HIV. In 2008, the region accounted for 67% of HIV infections worldwide, the region also accounted for 72% of the world’s AIDS-related deaths in 2008. Young people aged 15-24 years accounted for an estimated 45% of the new HIV infections. In sub-Saharan Africa, Kenya is among countries affected by the HIV and AIDS pandemic which led to the declaration of AIDS as a national disaster in 1999. Given these scenario the study was undertaken to examine trends in HIV and AIDS comprehensive knowledge and identify the main correlates of comprehensive HIV and AIDS knowledge among Kenyan urban young women. Methods: Data used was drawn from the 1993, 1998, 2003 and 2008/09 Kenya Demographic & Health Surveys. Logistic regression was used for analysis. Results: While comprehensive HIV and AIDS knowledge is low among urban young women in Kenya, the results show a significant increase in comprehensive knowledge from 9% in 1993 to 54% in 2008/09. The strongest predictors for having comprehensive knowledge were found to be 1) education; 2) having tested for HIV; 3) knowing someone with HIV, and/or 4) having a small or moderate to great risk perception. Conclusion: The response to HIV and AIDS can only be successful if individuals adopt behaviours that will protect against infection. Currently, efforts are underway in Kenya to ensure that young people have comprehensive knowledge. As evident from the results, comprehensive HIV and AIDS knowledge has increased over the 15 year period among urban young women from 9% in 1993 to 54% in 2008/09. Despite this improvement, a lot more needs to be done to attain the target of 90% threshold set by UNGASS. While both young women and men should be targeted with education on HIV prevention, concerted efforts should be directed at young women as many continue to get infected due to low levels of comprehensive HIV knowledge