An inguinal hernia is a common medical condition in daily practice. Indeed, the lifetimeprevalence of inguinal hernias is 47% in patients > 75 years of age, but it is rare to have metastatic cancer of an inguinal hernia sac. Most cases of intraperitoneal malignant inguinal hernias arise from the gastrointestinal tract. Extraperitoneal inguinal metastases most commonly occur in males with testicular cancer; there have been no reported cases that have metastasized from lung adenocarcinoma. Here we report a 77-year-old male with possible cancerous peritonitis that led to the finding of metastases in a hernia sac. The patient presented with disease progression after chemo-radiation therapy with multiple metastases to the liver and bone. This report highlights the importance of a pathologic evaluation of the inguinal hernia sac in preventing misdiagnosis.