By default, when adding ASP.NET Membership to your web app a new ASP.NET Membership database will be created. However, in many circumstances you may wish the Membership database to be part of your main application database. To do this simply navigate to \Windows\Microsoft.NET\Framework\v2.0.50727 (use this path even if you are using ASP.NET 4.0 in your application as the Membership database has not changed since ASP.NET 2).
Then find and run the aspnet_regsql.exe program. This will bring up a dialog allowing you to specify the target database to incorporate the ASP.NET Membership tables and stored procedures :
The final step is to ensure that the all connection string references to the membership provider in the web.config point to this database. Don’t forget if you are using Roles that the role provider specified in the web.config must also point to this database (otherwise ASP.NET will automatically create a new database for the roles when the app is run).