In "A General Theory of Crime", Gottfredson and Hirschi dispute whether valid self-report data can be collected among respondents lacking self-control. This research tests this argument by examining two processes that undermine the validity of self-report data: unit and item nonresponse. Specifically, this research addresses two questions: Within a longitudinal self-report study, are respondents with lower self-control less likely to be retained in annual follow ups? And are respondents with lower self-control less likely to complete a self-report survey in its entirety? These questions are examined with an adolescent sample from the National Evaluation of the Gang Resistance and Education Training Program. Current findings reveal that, after adjusting for the influence of student sociodemographic characteristics, self-control is unrelated to sample retention during four annual waves of data, but current findings do reveal that lower-self-control adolescents are more likely to leave survey items unanswered. Implications for the testing of self-control theory are explored. (Contains 4 tables and 16 notes.)