Actinomycosis is an uncommon bacterial infection that presents as an indolent, progressive disease that can affect multiple organ systems. We describe the case of a 66-year-old female with end-stage renal disease who presented to the emergency department after developing acute dyspnea and chest pain two weeks after undergoing a diagnostic esophagogastroduodenoscopy (EGD). A CT scan was obtained that revealed a large mediastinal mass, which was initially concerning for a potential malignancy. Biopsy of the mass and Gram stain was consistent with mediastinal actinomycosis. The patient was subsequently treated with an extended course of antibiotics that resulted in significant clinical improvement. Previously reported cases describing a correlation between EGD and mediastinal actinomycosis have been associated with invasive procedures such as esophageal stent placement and transesophageal biopsy. We describe a case of an uncommon infectious complication of a diagnostic EGD that was not associated with intentional mucosal disruption.