Tehran University of Medical Sciences Case Reports in Clinical Practice 2538-2683 4 1 2019 07 16 17 19 Mahnaz Pejman Sani Department of Internal Medicine, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. Mahbube Ebrahimpur Department of Internal Medicine, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran. Mahnaz Torki Department of Infectious Diseases, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. Neda Alijani Department of Internal Medicine, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran, Department of Infectious Diseases, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran. 2018 11 07 2019 01 22 Hydatid cyst is a parasitic infection caused by the larvae of Echinococcus granulosus. We report a rare case of primary echinococcal synovitis in a 37-year-old woman who was referred to our clinic with pain and swelling of the right knee. https://crcp.tums.ac.ir/index.php/crcp/article/view/234 https://crcp.tums.ac.ir/index.php/crcp/article/download/234/291