Objective: To examine the reliability of the Wolf Motor Function Test (WMFT) for assessing upper extremity motor function in adults with hemiplegia. Design: Interrater and test-retest reliability. Setting: A clinical research laboratory at a university medical center. Patients: A sample of convenience of 24 subjects with chronic hemiplegia (onset > 1yr), showing moderate motor impairment. Intervention: The WMFT includes 15 functional tasks. Performances were timed and rated by using a 6-point functional ability scale. The WMFT was administered to subjects twice with a 2-week interval between administrations. All test sessions were videotaped for scoring at a later time by blinded and trained experienced therapists. Main Outcome Measure: Interrater reliability was examined by using intraclass correlation coefficients and internal consistency by using Cronbach's alpha. Results: Interrater reliability was .97 or greater for performance time and .88 or greater for functional ability. Internal consistency for test 1 was .92 for performance time and .92 for functional ability; for test 2, it was .86 for performance time and .92 for functional ability. Test-retest reliability was .90 for performance time and .95 for functional ability. Absolute scores for subjects were stable over the 2 test administrations. Conclusion: The WMFT is an instrument with high interrater reliability, internal consistency, test-retest reliability, and adequate stability. © 2001 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation.