Hans Kooistra graduated in 1990 at the Faculty of Veterinary Medicine in Utrecht, The Netherlands. After working in a private practice for some time, he followed an internship and a residency in internal medicine of companion animals at the Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University (from 1991-1994). After the residency he became Assistant Professor (1994-2003), Associate Professor (2004-2018) and Full Professor (2018-…) at the same department. Since 2018 he is head of the division of Internal Medicine of Companion Animals. Duties include patient care, education (to students, post graduate training and training of interns and residents) and research in internal medicine of companion animals, with special emphasis on endocrinology and reproduction. In 1997 he became Diplomate of the European College of Veterinary Internal Medicine-Companion Animals (ECVIM-CA). He successfully (“cum laude”) defended his PhD thesis entitled “Adenohypophyseal function in healthy dogs and in dogs with pituitary disease” in December 2000. Hans is (co-)author of more than 170 peer-reviewed articles and several book chapters. In 1995 he married to Hilde. They have two children, David and Roselinde. Another important member of the family is their dog Twister.