The verb "to go" is inflected go/went/gone, as in "I go to at least one Rangers game each season," "I went to five Rangers games in 2010," and "I have gone to many Rangers games during the past 20 years."
By analogy, the verb "to forgo" (meaning "to do without; pass up voluntarily; waive; renounce") is inflected forgo/forwent/forgone, as in "I often forgo dessert," "I forwent dessert at Pappadeaux," and "I have forgone dessert many times in my life."
Don't confuse "forgo" with "forego," which means "to go before." A foregone conclusion is one that "went before" the premises: Everyone knew the conclusion before the premises were stated or grasped.
Keith Burgess-Jackson, J.D., Ph.D. 