Previous studies have indicated that certain illegal drugs are self-reported more readily than others. Respondents are typically more willing to report less serious drugs of abuse, such as marijuana, than they are "hard" drugs of abuse, such as cocaine. To date, however, no comprehensive analyses have examined whether the willingness to self-report illegal drugs fluctuates temporally. In the current study, we examine marijuana-, cocaine-, and heroin-positive Houston arrestees surveyed through the Arrestee Drug Abuse Monitoring (ADAM) Program between 1990 and 1997. Using Kappa statistics, we explore the temporal variation of self-reported drug use. Little variation is identified. Policy implications are assessed in light of the current findings.