Although individuals who attempt suicide have poor compliance rates with treatment recommendations, the nature and degree of participation bias in clinical treatment research among these individuals is virtually unknown. The purpose of this study was to examine participation bias by comparing the demographic and diagnostic characteristics of adult suicide attempters who participated in a randomized controlled trial to a sample of nonparticipants. Results indicated that males and individuals with a diagnosis of substance abuse or dependence were more likely to be participants in the randomized controlled trial. The implications of these findings for suicide intervention research are discussed.