Purpose: Rehabilitation nurses have essential responsibility for detailed Functional Independence Measure (FIM) documentation and accurate scoring. The goal of this performance improvement project was to improve individual FIM accuracy and establish and maintain a FIM accuracy standard. Design: Case Study. Methods: This performance improvement project was implemented in a 20-bed CARF-accredited Midwestern acute care hospital inpatient rehabilitation unit. Findings: Improved individual and overall RN FIM scoring accuracy, with increased length of stay and case mix index. Conclusions: Concurrent FIM scoring and documentation review holds staff accountable and allows for timely revisions following discrepancy identification. Leadership supports for concurrent FIM audits, utilization of available technology, transparent reporting of results, and individual accountability lead to sustained improvement in FIM scoring accuracy. Clinical Relevance: Accurate FIM documentation and scoring drive appropriate length of stay and case mix group assignment. Assessment competence enhances nursing engagement, confidence, and process accountability.