" The commonly mentioned figure of 20,000, however, is unreliable. For example, one sixteenth-century account states that 20,000 were sacrificed yearly in the capital city alone, another reports this as 20,000 infants, and a third claims the same number as being slaughtered throughout the Aztec empire on a single particular day. The most famous specific sacrifice took place in 1487 at the dedication of the main pyramid in Tenochtitlán. Here, too, figures vary: one source states 20,000, another 72,344, and several give 80,400."
I'm pretty sure it was 72,343 and 6 of those were lying about being virgins. [/sarcasm]
http://www.rose-hulman.edu/~delacova/aztecs/sacrifice.htm