The 2019 Kidney Tumor Segmentation Challenge (KiTS19) was one of several "grand challenges" associated with the 2019 International Conference on Medical Image Computing and Computer Assisted Intervention (MICCAI19) held in in Shenzhen, China. The challenge task was the develop an algorithm to automatically segment contrast-enhanced abdominal CT images into "kidney", "tumor", and "background" classes. To aid machine-learning-based approaches to this problem, 210 such CT scans were publicly released along with segmentation masks created manually by medical students under the supervision of an experienced urologic oncology surgeon. Teams were then asked to run their algorithm on a further 90 CT scans for which the manual segmentation masks were not available. Each team's output, or "predictions", for these 90 cases were uploaded to a web platform where they were automatically scored against the private manual segmentations. The challenge attracted submissions from 100 research teams around the world, and was won by Fabian Isensee and Klaus Maier-Hein at the German Cancer Research Center, who achieved a kidney Sørensen–Dice coefficient of 0.974 and a tumor Sørensen–Dice coefficient of 0.851. The prize for this challenge was $5,000 USD graciously provided by Intuitive Surgical. The lead organizer for this challenge was Nicholas Heller at the University of Minnesota, and he was aided by Niranjan Sathianathen, Arveen Kalapara, Christopher Weight, and Nikolaos Papanikolopoulos. The organization of this challenge was funded by the non-profit "Climb 4 Kidney Cancer" as well as the National Cancer Institute of the National Institutes of Health under award number R01CA225435.