Pulmonary lymphangitic carcinomatosis (PLC) is defined as infiltration of the lymphatic vessels and perilymphatic connective tissue with tumor cells, which is secondary to malignancy. Therefore, it rarely appears as an initial finding preceding a diagnosis of malignancy. A 30-year-old male patient was hospitalized in our clinic with a pre-diagnosis of interstitial lung disease owing to the complaints of dry cough, progressive dyspnea, and acute respiratory insufficiency. He was diagnosed with signet ring cell carcinoma, which is a histologic subtype of adenocarcinoma, via gastroscopy, and lung involvement was consistent with PLC. Regardless of the patient age, PLC should be considered in differential diagnoses of progressive dyspnea, acute respiratory failure, and widespread interstitial lung involvement.