Background: Spasticity is present among 60-80% of individuals with Multiple Sclerosis (Etoom et al, 2018). One-third of people with Multiple Sclerosis (MS) may experience spasticity that negatively impacts their quality of life (Hughes & Howard, 2013). Long arm serial casting (LASC; upper arm to fingers) is found in the literature for individuals with brain injury and stroke. No publications for LASC were found for individuals with MS. Objectives: To evaluate if LASC would decrease upper extremity spasticity and improve function in a 52 y.o. woman with Relapsing Remitting MS. Methods: All evaluations and treatment interventions of the right upper extremity (RUE) were performed by a licensed occupational therapist. Serial casting involves a series of casts which are applied and removed with the goal of increasing range of motion (ROM) with each cast. The final LASC is then turned into a bivalve cast by cutting it in half to allow for daily application and removal. The participant presented with spasticity and nonfunctional use of RUE. She had very limited functional use of her right hand, elbow, and shoulder. Modified Tardieu, Modified Ashworth Scale (MAS), pain, strength, passive range of motion (PROM), skin, and function were assessed. The intervention totaled 9 visits after conservative measures were found to be ineffective over visits 1-8: Visit 9 consultation/education for LASC, visits 10-12 LASC and bi-valve fabrication, and visits 13-17 continued use of bivalve in combination with neuromuscular re-education, strengthening and functional training. The participants disease modifying therapy was Ocrevus, but no infusions took place during the intervention. Results: Spasticity and PROM improved. Increased strength was found in shoulder flexion, elbow flexion/extension, and supination. Active shoulder range of motion, not possible pre-intervention due to pain, was possible and pain free post-intervention for abduction, horizontal abduction, horizontal adduction, and external rotation. Furthermore, increased functional use including feeding, dressing, and bathing was achieved. Conclusions: Long arm serial casting may be an effective intervention for individuals with MS who have debilitating upper extremity spasticity. To the writers knowledge, there is no published research regarding LASC for individuals with MS. Additional research is warranted.