Tehran University of Medical Sciences Iranian Journal of Parasitology 1735-7020 21 3 2026 09 02 426 433 EN Ehsan Adib 1. Students Research Committee, School of Medicine, Ardabil University of Medical Sciences, Ardabil, Iran 2. Cancer Immunology and Immunotherapy Research Center, Ardabil University of Medical Sciences, Ardabil, Iran Zahra Heidari Department of Medical Microbiology, Parasitology and Immunology, School of Medicine, Ardabil University of Medi-cal Sciences, Ardabil, Iran Mohammad Vakili Ojarood Department of Surgery, School of Medicine, Ardabil University of Medical Sciences, Ardabil, Iran 2025 12 24 2026 09 02 Hydatid cyst disease is a common disease in humans and animals. In livestock and agricultural areas, it is caused by the tapeworm Echinococcus. Canines serve as the definitive host, while livestock act as the intermediate host for this parasite. Humans can also be infected with the eggs of this parasite as accidental hosts, and in most cases, the liver and lungs are the primary sites of infection with this parasite and its cysts. In rare cases, other organs such as the spleen can also be infected with this cyst. Its rarity as well as the nonspecific clinical manifestations of splenic hydatid cysts lead to delays in its diagnosis and treatment. Ardabil province in northwestern Iran is one of the largest livestock-breeding areas in Iran, contributing to the spread of Echinococcosis in this region. This case report discusses a 47-year-old female farmer from Ardabil Province who, following 2 years of chronic pain in the left upper quadrant of her abdomen and splenomegaly, was diagnosed with a 13×10×10 cm isolated hydatid cyst of the spleen without involvement of other organs according to paraclinical examinations (e.g., ultrasound, CT scan, Indirect hemagglutination test). Finally, she underwent total splenectomy due to the large size of the cyst and the risk of rupture without any complications, and a histological examination confirmed the diagnosis. https://ijpa.tums.ac.ir/index.php/ijpa/article/view/4857 https://ijpa.tums.ac.ir/index.php/ijpa/article/download/4857/1519