OBJECTIVE: To quantify the relationship between the Spinal Cord Independence Measure III (SCIM III), arm and hand muscle strength, and hand function tests in persons with tetraplegia. METHODS: A total of 29 individuals with tetraplegia (motor level between cervical 4 and thoracic 1; sensory-motor complete and incomplete) participated. The total score, category scores, and separate items of the SCIM III were compared to the upper extremity motor score (UEMS), an extended manual muscle test (MMT) for 11 upper extremity muscles, and 6 functional capacity tests of the hand. Spearman's correlation coefficients (rs) and regression analyses were performed. RESULTS: The SCIM III sum score correlated well with the sum scores of the 3 tests (rs >/= .76). The SCIM III self-care category correlated better with the tests (rs >/= .80) compared to the other categories (rs </= .72). The SCIM III self-care item "grooming" highly correlated with muscle strength and hand capacity items (rs >/= .80). A combination of hand muscle tests and the key grasping task explained over 90% of the variability in the self-care category scores. CONCLUSIONS: The SCIM III self-care category reflects upper extremity performance as it contains especially useful and valid items that relate to upper extremity function and capacity tests.