Histiocytic sarcomas are malignant tumors of tissue macrophages that comprise an incredibly rare group of hematopoietic neoplasms. Investigation of historical diagnoses of histiocytic sarcoma reveals misclassifications of B-cell neoplasms and anaplastic large cell lymphomas, making the true diagnosis of histiocytic sarcoma even more rare than previously recognized. Histiocytic sarcomas are diagnosed by histology, morphology, and immunohistochemistry. They often manifest with extranodal presentations that are typically cutaneous or gastrointestinal in origin. We present the fifth documented case of primary pulmonary histiocytic sarcoma that developed in a 61-year-old man and manifested as hemoptysis with interval development of hemothorax. Prognosis is poor and the rarity of histiocytic sarcomas preclude the establishment of standardized treatment guidelines.