Comparison for monthly reports.... accounts added and removed

I need to create a spreadsheet that will compare monthly reports from one month end to the next. The reports include account numbers that fluctuate. One month account #s 1,2,3,4,5,6 may be on the report and the next month account #s 3,4,5,6,7,8 may be on the report.

I need to be able to sort out which accounts were removed the new month and which were added on.

I have a spreadsheet for each month with several columns of information for each account. I'm trying to figure out how I can do what I want to do without manually comparing side by side... inserting rows... cutting/pasting etc.

Any ideas?