BACKGROUND: This study explored the factors associated with changes in HIV testing uptake among young women in Tanzania, based on an analysis of data from the 2003-2004 Tanzania HIV/AIDS Indicator Survey, and the 2007-2008 and 2011-2012 Tanzania HIV/AIDS and Malaria Indicator Surveys. METHODS: The study population consisted of young women aged 15-24 years at the time of the survey. Multivariate decomposition analysis was used to assess factors associated with changes in HIV testing uptake between the 2003-2004 and 2007-2008 surveys, and between the 2007-2008 and 2011-2012 surveys. RESULTS: HIV testing uptake among the study population was 7 % in 2003-2004, 31 % in 2007-2008 and 40 % in 2011-2012. The time period of the survey had a substantial effect on the uptake of HIV testing independent of other covariates. The characteristics that were significantly associated with a higher chance of HIV testing uptake across the surveys were age (20-24), education level (primary and secondary), ever being married, having at least one lifetime sexual partner, having a sexually transmitted infection or associated symptoms, and receiving antenatal care. CONCLUSIONS: Changes in the study participants' characteristics in the 2003-2004 survey compared with the 2007-2008 survey were associated with a decrease in HIV testing uptake. Comparing the 2007-2008 survey with the 2011-2012 survey shows that the changes in the participants' characteristics contributed to 22 % of the changes in HIV testing uptake, while 78 % of the changes were attributed to coefficients.