Background: Multiple sclerosis (MS) is a chronic neurological disorder and a major cause of disability in young adults. Cladribine tablets received approval in the United States (US) in March 2019 and are indicated for the treatment of relapsing forms of MS. The dosage of cladribine tablets is 3.5 mg/kg over 2 years with 1.75 mg/kg being administered each year. Cladribine tablets are thought to work as an immune reconstitution therapy with clinical efficacy sustained beyond total lymphocyte recovery suggesting a qualitative immune change that may persist long after the last cladribine tablet dose. Objectives: To describe treatment patterns for cladribine tablets in a real-world US setting. In the phase 3 clinical trials patients were either treatment naïve or transitioned from platform injectable therapies. The goal of this study is to present early real-world experience in patients initiating cladribine tablets with prior use S1P or infusion disease modifying therapies (DMTs). Outcomes include patient characteristics at treatment initiation, previous DMT use, tolerability and safety, lymphocyte dynamics and preliminary efficacy data. Methods: none Results: In all, 48 patients have initiated therapy with cladribine tablets following prior treatment with a S1P (n=31) or infusion (n=17) DMT. Mean age at cladribine tablets initiation was 49.7 years (range 26-67) with mean disease duration of 15.6 years (range 1-37). Relapses occurred in 6 patients (12.5%) following cladribine tablets initiation with a mean follow-up of 268.9 days. Lymphopenia has been observed in 37 patients (77.1%) with no patients experiencing grade 4 lymphopenia. One patient (2.1%) stopped therapy because of adverse events (AEs). Conclusions: The use of real-world data will continue to complement the knowledge gained from randomized controlled trials and help inform therapeutic development, contribute to safety surveillance, and identify which patients will benefit most from a certain treatment. In this cohort of patients starting cladribine tablets, treatment was well tolerated with a side effect profile generally reflecting findings from the clinical trial program. Ongoing follow up will further refine and expand on these results as more patients complete 2 full treatment courses of cladribine tablets.