BACKGROUND Gastric adenocarcinoma is a common malignancy, representing the third most common cause of cancer-related death globally. Most patients are initially asymptomatic, but as the cancer progresses, patients typically present with vague gastrointestinal complaints, including early satiety, heart burn, vomiting, or abdominal pain. Metastatic gastric cancer is relatively uncommon, with ~26% of patients having metastasis to a single site and 13% having metastases to multiple sites. The most common site of metastasis is the liver, followed by peritoneum, lung, and bone. CASE REPORT In this case report we describe a 73-year-old man who presented with shortness of breath, found to have large hiatal hernia along with segmental branch pulmonary embolism, bilateral pleural effusion, and diffuse interlobular septal thickening. The pleural effusion was later found to be malignant in nature and the patient was diagnosed with metastatic stage IV infiltrative gastric adenocarcinoma with metastasis to the lung and bone. Notably, the patient had no hepatic involvement. CONCLUSIONS This represents a unique case, as only 2% of malignant pleural effusions are attributable to gastric cancer. Furthermore, malignant pleural effusion is an extremely rare initial presentation of gastric adenocarcinoma, especially without liver involvement, with few existing cases documented in the literature. This case demonstrates that gastric cancer should be included on the differential diagnosis as a rare cause of pleural effusion.