This 2011-12 Tanzania HIV/AIDS and Malaria Indicator Survey (THMIS) was implemented by the National Bureau of Statistics (NBS) in collaboration with the Office of the Chief Government Statistician (OCGS-Zanzibar) from December 16, 2011, to May 24, 2012.The Tanzania Commission for AIDS (TACAIDS) and the Zanzibar AIDS Commission authorized the National Bureau of Statistics (NBS) to conduct the 2011-12 THMIS. The survey covers both the Tanzania Mainland and Zanzibar. The objectives of the 2011-12 THMIS were to collect data on knowledge and behaviour regarding HIV/AIDS and malaria, measure HIV prevalence among women and men age 15-49, and measure the presence of malaria parasites and anaemia among children age 6-59 months. The 2011-12 THMIS follows up on the 2007-08 THMIS and the 2003-04 Tanzania HIV/AIDS Indicator Survey (THIS). The 2011-12 THMIS also updates estimates of selected basic demographic and health indicators covered in previous surveys, including the 1991-92 Tanzania Demographic and Health Survey (TDHS), the 1996 TDHS, the 1999 Reproductive and Child Health Survey, the 2004-05 TDHS, and the 2010 TDHS.