Supporting and retaining U.S. K-12 beginning teachers remains a problem and has been linked to early career stress. Although teacher induction programs for beginning teachers have flourished in recent decades, beginning teacher stress persists and can undermine their occupational health. Teacher mentoring has been identified as an important way to support beginning teachers. To add to the literature in this area, the present study examines associations between mentoring experiences and first-year teacher stress. Using 1,980 responses to the 2007-08 Beginning Teacher Longitudinal Survey, scale scores were created for teacher appraisals of demands and resources and mentoring frequency and helpfulness. Teachers who identified classroom demands as exceeding resources (32.8%) reported significantly fewer (d = 0.20) and less helpful mentoring experiences (d = 0.19) than teachers rating demands and resources as equal. Teachers with higher resources than demands (21.9%) reported significantly greater (d = 0.20) and more helpful mentoring experiences (d = 0.32).