iTunes 12.0 offers a simple way to track down and find duplicate songs in a music library:
1 Open the “iTunes” app if you have not done so already
2 Go to your music library in iTunes
3 Pull down the “File” menu and then go to “Library”
4 From the “Library” sub-menu, choose “Show Duplicate Items”
5 iTunes will gather a list of potentially duplicate songs that you can peruse through and verify independently
Once finished, you can click the “Done” button at the Display Duplicate screen to go back to the regular track listing of your iTunes library.
iTunes will show as “duplicates” two different versions of the same song if they share the same track name, even if the songs and files are actually totally different. This is important to understand, particularly if you have a lot of music from the same artist, with live albums, Greatest Hits collections, or remixes and so forth.
use the song “Time” column to see how long each track is. If the tracks are the exact same length, it’s more likely the songs are actually the same and not just different recordings with the same name. Also be sure to pay attention to the Album name too, since that can be a helpful indicator.
Go here for iTunes 11.0.1