Objectives. The authors examine perceptions of a peer’s substance use to determine whether and to what degree individuals project their own behavior onto their perceptions of peer’s delinquency, and to determine whether the constructs of self-control and peer attachment are related to perceptions. Methods. Using a sample of 2,154 young adult respondents within friendship pairs in which each respondent reported their own substance use and their perception of the friend’s use, the authors estimate a series of regression models with perceptions of a peer’s alcohol, marijuana, Salvia divinorum, and hard drug use as dependent variables. Results. Perceptions of a peer’s substance use are approximately equally related to a peer’s and a respondent’s use of each substance. Projection occurs to a greater extent when perceiving low-frequency behaviors. Low self-control is sporadically associated with higher perceived substance use. Conclusions. Peer self-reported delinquency and perceptions of peer delinquency are distinct constructs. Because projection appears to be worse for infrequent behaviors, researchers should use caution when using low-frequency behaviors to measure perceptual peer delinquency. Although the data used are cross sectional, the perceptual measure is confounded by too many variables other than a peer’s actual delinquency to be considered a valid measure of the sole construct of peer delinquency.