In reviewing cutaneous manifestations of various hematologic malignancies, the authors focus on secondary cutaneous lymphomas and cutaneous manifestations of histiocyte disorders. Secondary cutaneous lymphomas are defined as skin lesions that develop secondary to infiltration by systemic lymphomas with predominantly extracutaneous involvement. In their review of histiocytic disorders with skin involvement, the authors focus on Langerhans cell histiocytosis and Rosai-Dorfman disease. Their review emphasizes the histology, pathophysiology, clinical presentation, prognosis, and treatments available for these diseases.