When you are choosing your anniversary party ideas for parents there are a few things that you need to think about;
Big, surprise parties are not for everyone and a lot of couples will be happier that their closest family and friends are there to help them celebrate on a smaller scale.
Choosing the party theme, invitations and decorations is so much easier if you stick with the anniversary symbol for your party. Of course you don't have to, you may want to base the party on the decade they were married or around their favorite hobby. Or this party could be the wedding reception that they wanted but never had.
However many guests you want to invite to your parents' anniversary party you will want the venue to be able to hold the number comfortably and that is the same whether you have hundreds or just 10 people. You don't want the room to be too big otherwise your guests will be awkward, you would be better off booking a table at a restaurant rather than a function room if your numbers are small.
If you have hundreds of guests or a larger number than you would be able to have at your home then a hall or a function room in a local hotel will be ideal. If your parents are members of a club then they may want to have their anniversary party there as they are familiar with the club and probably a large number of their friends will be too!
You may find that your parents are planning on going away for their anniversary, they may want to go on a cruise, or revisit where they spent their wedding night. If that is the case then you may find that you will need to have the party before or after the big day.
As with planning a wedding you may want to send out save the dates for your parents' anniversary party or send the invitations with enough time. Six weeks before the event is a good idea but if your party is during holiday time or popular summer vacation time then you will want to send them out earlier.