Although much is known about the nature of supportive behaviors during organizational socialization, less is known about the effects of undermining during this process. This study examines the effects of undermining from peers and supervisors on organizational newcomers during the early stages of socialization. It examines these effects on select outcome variables (organizational commitment, withdrawal behaviors, coworker satisfaction, burnout, and thriving) via a two-stage mediation process model that includes proactive socialization, newcomer adaptation, role clarity, and social acceptance as mediating variables. The effects were examined using structural equation modeling, and the results indicate that undermining in general does have deleterious effects on the outcomes via the mediational processes, but that the relationships are complex. Implications for the findings and future directions are also highlighted.