Pornography is Part of the Word of Wisdom
President Gordon B. Hinckley

Very recently a certain moving picture was acclaimed the best of the year. I have not seen it, nor do I anticipate doing so. But I am told that it is laden with sex, that the use of profanity runs throughout.
Pornography is one of the hallmarks of our time. Its producers grow rich on the gullibility of those who like to watch it. In the opening lines of the revelation which we call the Word of Wisdom, the Lord declares, "In consequence of evils and designs which do and will exist in the hearts of conspiring men in the last days, I have warned you, and forewarn you, by giving unto you this word of wisdom by revelation" (D&C 89:4).
He then goes on to talk about the food we put into our mouths. The same language might be applied with reference to that which we take into our minds when we indulge in pornography.

(President Hinckley, CR, April 2003, p. 63)

Section 89

Doctrine & Covenants