Much of the limited literature on organ donation has focused on the demographic and psychographic profiles of people who are willing to become organ donors. More information about the relationship of attitudes, values, knowledge, and actual behavior among adults is needed if targeted communication campaigns promoting organ donation are to succeed. The results of a mail survey of 798 adults sampled (via stratified random sampling procedures) from two local sites of a national corporation suggest that attitudes toward donation, knowledge about organ donation, altruism, and perceived social norms are significantly associated with both actual behavior (having signed an organ donor card) and behavioral intent (among non-donors) to sign a card in the future. These findings support the major models of organ donation willingness, especially those advanced by Horton and Horton (1991) and Kopfman (1994). This study also advances current knowledge of organ donation willingness by 1) using a large, relatively diverse population of adults rather than relying on a student sample; and 2) focusing on specific knowledge barriers that distinguish donors from non-donors.