Is there a way to add custom fields to include in the site registration and store in the account database?

Thanks.

In DNN 4.x you actually have TWO options for making a user profile field required (works the same for existing profile fields and for custom-created fields):

1. Require valid profile during account creation.
    
2. Require valid profile during next login.

 
For #1, any profile fields marked as "required" will be presented to the user during the account registration process.  This means that existing users with accounts are not required to fill out the field(s) newly marked as "required".
 
For #2, an account can be created without all the "required" user profile fields (though "user credential" fields are still required).  However, upon the user's next login, the user will be prompted for the "required" profile fields (this is a little confusing).
 
So, to make any profile field "required" for both existing and new users, enable both #1 and #2.

I have not played with this in 5.x but I'm not aware of any change for these options (so far).
 
-mamlin