The introduction of immune checkpoint inhibitors has revolutionized cancer treatment. These drugs function by inhibiting the binding of programmed death-1 (PD-1) and its ligand, PD-L1, which inhibits the immune response against cancer cells. Nivolumab is a PD-1 inhibitor that specifically targets the PD-1 pathway. The main side effects of these drugs are unpredictable immune-related toxicities that occur when self-reactive T cells are abnormally activated and cause inflammation in various organs. The organs most often affected are the endocrine glands, lungs, skin, and gut. Recognizing and addressing lung inflammation is crucial, particularly in individuals with lung cancer. However, it can be challenging to diagnose due to the distinctive features of their disease and treatment regimen.This case report presents a 66-year-old man with a medical history of hypertension, chronic kidney disease (stage 3A), hypothyroidism, type 2 diabetes mellitus (DM), and transitional cell carcinoma of the bladder with interstitial pneumonitis secondary to nivolumab. The patient presented to the Eisenhower Medical Center, Rancho Mirage, CA, with dyspnea and cough for two weeks. He received methylprednisolone (Solu-Medrol) at 1.0 mg/kg for immune checkpoint inhibitor-induced pneumonitis and was discharged on 1 liter (L)/min home-oxygen therapy along with prednisone 50 mg twice daily (BD) for six weeks, trimethoprim-sulfamethoxazole (Bactrim) DS BD, and pantoprazole (Protonix) 40 mg once daily. Subsequently, nivolumab therapy was discontinued. At his follow-up visit two weeks later, he felt well and did not need oxygen therapy at rest.