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Background: Ocrelizumab (OCR) is an anti-CD20 monoclonal antibody approved for the treatment of relapsing-remitting and primary-progressive multiple sclerosis (MS). We aimed to evaluate the effectiveness of an individualized OCR extended interval dosing (EID), after switching from standard interval dosing (SID). Methods: This was a retrospective, observational, single-centre study including MS patients regularly followed at the Neurocenter of Southern Switzerland. After a cumulative OCR dose ⩾1200 mg, stable patients were switched to EID (OCR infusions following CD19+ 27+ memory B cell repopulation). Results: A total of 128 patients were included in the study, and 113 (88.3%) were switched to EID with a median interval of 9.9 (8.8–11.8) months between infusions. No clinical relapses occurred; 2 (1.8%) patients experienced disability worsening. Three (2.7%) and 2 (1.8%) patients experienced new T2 brain and spinal lesions, respectively. There was a mild decrease in IgG and IgM concentrations during both SID and EID OCR regimens (β = −0.23, p = 0.001 and β = −0.07, p < 0.001, respectively). Conclusion: Switch to personalized dosing of OCR based on CD19+ 27+ memory B cell repopulation led to a great extension of the interval between infusions, with maintained clinical and radiological efficacy. Given the potential advantages in terms of safety and health costs, EID OCR regimens should be further investigated. [ABSTRACT FROM AUTHOR]