What is the leading cause of death in the world?

Infectious Diseases are the leading cause of death worldwide, and the number of deaths from infectious diseases in the United States has been increasing. Infectious diseases ranked third among the leading causes of death in 1992 in the United States.

Acquired Immune Deficiency Syndrome (AIDS) is the leading cause of death in Sub-Saharan Africa and the fourth leading cause of death worldwide.

http://www.cdc.gov/nceh/ierh/Publications/hiv_aids_pib.htm