I am the fiduciary of an irrevocable trust. There were attorney fees incurred in 2016 to defend the trust. Are they deductible?

Most certainly, such attorney or accountant fees are deductible.  This is true as long as they were spent in an effort to defend the trust instrument itself; protect the beneficiaries of the trust; administer or manage the trust; or incurred in the pursuit of earning taxable income (such as would be the case in a legal action undertaken for collecting unpaid rent, for example, if the trust owned rental property).

Such costs are directly deductible on Form 1041, Line 14; please see the attached screen-capture image for a visual illustration (simply click the image to open).

Thank you for asking this important question.