In English, we always use the plural form "pants". Is it common usage in Spanish to say "el pantalón" to mean one pair of pants? And does "los pantalones" mean multiple pairs of pants?
It may be different in different places, but I am from Spain and we say both "el pantalón" and "los pantalones" to mean one pair of pants (always "los pantalones" if plural, though), no distinction.
I'm from Mexico, and we also use "el pantalón" and "los pantalones" to refer to a single pair of pants, as babella says.
There's a great vid on the entemology of pants here: http://ed.ted.com/lessons/mysteries-of-vernacular-pants-jessica-oreck
Now I'm curious if Pantaleonis or Pantaloons were singular or plural. :P