Late-onset neutropenia (LON) after anti-CD20 therapy is a poorly described side effect in inflammatory disorders of the CNS. In this prospective study, patients treated with Rituximab or Ocrelizumab for MS, neuromyelitis optica spectrum disorders or MOG antibody-associated disease (MOGAD) were asked to perform complete blood count (CBC) every two weeks for six months, with the aim of identifying LON. Out of 152 patients, two (1,32%) had an absolute neutrophil count <1,000/mm3: one patient with MOGAD had agranulocytosis and one patient with MS had grade 3 neutropenia. Both were asymptomatic. These results confirm that LON after anti-CD20 therapy in inflammatory disorders of the CNS is not exceptional. Nevertheless, this biological complication remains too infrequent to justify close systematic CBC follow-up.