OBJECTIVES: To assess the impact of shift work on health care workers. SUBJECTS AND METHODS: A cross-sectional study assessed health and performance markers of 188 day and night shift nonphysician health care workers. RESULTS: Night-shift workers were more likely to report difficulty with routine orders, lower energy levels, unpredictable work schedules, and sleep disturbance but no difference with injuries or motor vehicle crashes. A classification of day shift, night shift without unpredictable schedule or sleep problems, and night shift with unpredictable schedule or sleep problems revealed a trend of increased difficulty with routine orders, suggesting a "dose response effect." CONCLUSIONS: Findings suggest an association with night shift health care workers and adverse health and performance markers. A "higher-risk" subgroup may benefit from targeted interventions to reduce potential adverse effects from shift work and improve health care delivery.