The anti-programmed cell death-ligand 1 (PD-L1) antibody atezolizumab is a promising agent for various cancers. Although immune-related adverse events (irAEs) induced by atezolizumab are rare, they can be severe. Clinical experience in irAE management is presently insufficient. Herein, we present a case of a patient with non-small cell lung cancer (NSCLC) who developed life-threatening irAEs including pneumonitis, thrombocytopenia, and cardiac dysfunction under immunotherapy with atezolizumab. Under expectant treatment and corticosteroid regimen, pneumonitis was totally resolved. However, thrombocytopenia and cardiac dysfunction did not improve. The patient sadly passed away 28 days after a single dose of atezolizumab. This case alarmed us once more to the importance of irAE management under cancer immunotherapy. .