Thoracic splenosis is a rare entity resulting from splenic and diaphragmatic injury. Patients remain asymptomatic, and surgical intervention is not indicated in the majority of cases. We report a case of a 50-year-old male with a history of splenectomy due to a gunshot wound 30 years previously who presented with vague, progressively worsening chest pain. He was found to have a large intrathoracic splenosis. Unique features of our patient include the presence of symptoms, the significant interval growth of the splenic tissue, and the unprecedented size of the mass, which we believe to be the largest among those previously described.