Checkpoints inhibitors anti-programmed death 1 (PD1) and anti-programmed death ligand 1 (PD-L1) restore immunity against tumour. By their mechanism of action, they could induce immune-related adverse events (irAEs) that can theoretically involve all organs. These irAEs, especially those that are rare, remain incompletely described. Immune-related eosinophilia has been described with ipilimumab and was interestingly associated with favourable response to immunotherapy. We report here the first series of patients who experienced immune-related eosinophilia due to anti-PDI or anti-PD-L1 antibodies. Immune-related eosinophilia is a new biological immune-related adverse effect with anti-PD-1 or anti-PD-Ll. To the best of our knowledge, we report here the first case series of immune-related eosinophilia with anti-PDl or anti-PD-Ll. Importantly, we show that kinetics of leukocyte changes was restricted to the eosinophil lineage. This immune-related eosinophilia was rare (estimated frequency of 2.9%), began at 3.0 months with a peak achieved at 6.4 months. Patients with immune-related eosinophilia remain asymptomatic. Larger prospective studies are required to search for a link with favourable anti-tumour response.