Purpose/Objective: To develop and test initial validation of a theory-driven quantitative measure of identity reconstruction in patients with multiple sclerosis (MS) based upon previous qualitative research. Research Method/Design: This study uses a cross-sectional survey design, in which 137 patients living with MS were recruited from an outpatient MS Center in the Southeastern U.S. Participants completed demographic items, Identity Reconstruction Assessment Scales (IRAS), Patient Determined Disease Steps, Medical Outcomes Study Measures of Patient Adherence, Chronic Disease Self-Efficacy Scale, Hospital Anxiety and Depression Scale, Leeds MS Quality of Life Questionnaire, MS-Related Stigma Scale, and Posttraumatic Growth Inventory—Short Form. Results: The IRAS conformed to a 3-factor solution consisting of 23 items accounting for 42.6% of the variance. The 3 factors, labeled as “sustained identity” (α = .84), “reactionary identity” (α = .74), and “integrated identity” (α = .65), were not significantly correlated with each other, necessitating and allowing for independent scoring of the scales. Higher scores on “sustained identity” scale were associated with less anxiety, depression, perceived disability, and MS-related stigma, as well as with increased self-efficacy, treatment adherence, and quality of life. “Reactionary identity” scale was positively correlated with anxiety and MS-related stigma. “Integrated identity” was significantly associated with age and perceived disability. Conclusions/Implications: Identity reconstruction provides needed context for understanding adjustment to and living with MS. Examination of the IRAS within a larger sample and in other disease groups can provide additional construct validity evidence.