Depends on what service it is. If you are getting an error uninstalling from the Add/Remove option in Control Panel, it means files have been deleted that the uninstall program required. You may have to reinstall the program to uninstall it.
Services are installed as part of NT and also as part of apps. When you uninstall an app, it will remove the required service. "My mamma used to say that life is like a box of chocolates .... you never know what you're gonna get!"