In peer nomination research, individuals who do not provide nominations (nonparticipants) are often included on rosters as potential nominees. This can present ethical questions regarding informed consent, but psychometric consequences of excluding nonparticipants from rosters are unknown. In this investigation, Study 1 simulated both random and systematic missingness with a sample of 1,630 Dutch adolescents, comparing the reliability and correlation matrices of nomination measures when nonparticipants were included and excluded as nominees. Study 2 began with a two-school sample that already included systematic nonparticipation (˜19% missingness among 599 7th grade nominees) and examined how findings would differ if students who had not provided nominations were excluded as nominees. Results showed that the impact of including versus excluding nonparticipants as nominees may vary depending on the type of missingness (Study 1) or in different peer groups (Study 2). Both studies demonstrated that the choice of including versus excluding nonparticipants can affect reliability and intercorrelations in peer nomination data, and provide some evidence that excluding nonparticipants as nominees may compromise peer nomination data quality.