Description of a patient with multiple sclerosis (MS) who underwent immunotherapy with ocrelizumab and suffered a severe course of tick-borne encephalitis (TBE): A 33-year-old man presented with acute cerebellitis with tonsillar herniation. The initial suspected diagnosis of TBE was confirmed after a significant diagnostic delay, likely caused by negative serological testing due to B-cell depletion from ocrelizumab treatment for underlying MS. TBE diagnosis was made using polymerase chain reaction (PCR) and oligo-hybrid capture metagenomic next-generation sequencing (mNGS) of cerebral spinal fluid and brain biopsy samples which yielded a near-full length TBE Virus (TBEV) genome.