See http://blogs.msdn.com/fxcop/archive/2006/04/05/faq-why-do-some-sources-recommend-extending-applicationexception-while-fxcop-does-not-michael-fanning-david-kean.aspx. The use of ApplicationException, while not depreciated, is not recommended. As such, raised strings should be wrapped in an Exception instead to keep in compliance with FXCop recommendations: DoNotRaiseReservedExceptionTypes and TypesShouldNotExtendCertainBaseTypes If the user chooses to raise a string, then it will still fail DoNotRaiseReservedExceptionTypes due to the Exception being thrown, though it is more in compliance with moving away from ApplicationExceptions