Fever caused by internal injury is the product of stagnant liver heat, insufficient middle qi, deficiency of qi, blood and essence, and obstruction of phlegm and blood stasis that result in the disharmony of internal organs. The etiology includes emotional stress, diet, fatigue, heredity, chronic condition, and bleeding due to external injury. The mechanism includes disharmony of internal organs and deficiency of qi, blood and essence. The clinical manifestations are chronic onset and longer course of disease. Common symptoms include low fever, but sometimes high fever. Treatment based on pattern differentiation includes: modified DanZhiXiaoYaoSan for stagnant liver qi; modified XueFuZhuYuTang for blood stasis; modified SanRenTang for obstruction of dampness; modified BuZhongYiQiTang for deficiency of qi; modified GuiPiTang for deficiency of blood; modified QingGuTang for deficiency of Yin; modified JinKuiShenQiWan for deficiency of Yang.