If in doubt, you could reword it saying, "the 50th Wedding Anniversary of our parents." It really irks me when people put the apostrophe in the wrong place or overuse it.
By
10/29/2009
Since you are talking about both parents; parents' is correct.
By
10/29/2009
Yes, parents' is correct! Have a great celebration! What wonderful role models they are for all of us!
By
10/27/2009
That'd be "parents' 50th." The "s" makes it plural, the apostrophe after the "s" shows ownership. And hey -- I hope the celebration is wonderful! My parents are up to 41 years. :-)