This report examined the stability and reliability of self-reported conflict frequency in relationships with mothers, fathers, and best friends. Participants were drawn from three independent samples in the Netherlands (n = 72, M = 15.6 years), Germany (n = 242, M = 19.7 years), and the United States (n = 250, M = 19.8 years). Participants completed both topic-based surveys and interaction-based diary assessments of conflict frequency. Within samples, comparable levels of internal consistency and temporal stability emerged in each relationship for both assessment techniques. Topic-based and interaction-based assessments of conflict frequency were moderately correlated in each relationship within samples. Daily topic-based assessments with short intervals between time points may provide the most advantageous assessment strategy for obtaining reliable measures of conflict frequency in adolescents’ close relationships.