Karl Ernst Ranke (29 January 1870 in Munich – 9 November 1926 in Munich) was a German internist, pediatrician and pulmonologist known for his research of tuberculosis. He was the son of anthropologist Johannes Ranke (1836–1916).
In 1896 he received his medical doctorate from the University of Munich, then spent the following year as an assistant to his uncle, Heinrich von Ranke (1830–1909), at the pediatric clinic in Munich. Afterwards, he was in charge of an anthropological research expedition to Brazil. Following his return to Germany, he spent two additional years as an assistant in the pediatric clinic, then relocated to Arosa, Switzerland, where he worked as a doctor in a tuberculosis sanatorium. 
In 1906, he returned to Munich, where he practiced pediatrics, and specialized in diseases of the lung. In 1915 he earned his habilitation in internal medicine at Munich, and in 1921 became an associate professor. At Munich, he was director of the "Fürsorgestelle für Lungenkranke". During the last decade of his life, he immersed himself in the philosophy of Immanuel Kant.
He is remembered for introducing the hypothesis that lung tuberculosis develops in three stages — referred to as "Ranke Dreistadienlehre" (also known as "Ranke's stages of tuberculosis"). His name is also associated with the so-called "Ranke complex", defined as a combination of late fibrocalcific lesions of the lung and lymph node that evolve from the Ghon complex.
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