A public method or constructor that throws an exception but does not have a documentation tag for the exception makes an API more difficult to understand and maintain.

The documentation comment for a method or constructor should include an <exception> tag that describes each thrown exception, and the cref attribute of the tag should match the type of the exception that is thrown.

The following example shows a good documentation comment, which clearly explains the method's thrown exception.

MSDN, C# Programming Guide: XML Documentation Comments, How to: Use the XML Documentation Features, Recommended Tags for Documentation Comments.