Hydatid disease (HD), also known as echinococcus or hydatidosis, is a serious health problem in areas in which it is endemic. HD has a characteristic geographic distribution. Our country is an endemic region for this disease. Echinococcus granulosus is the causative agent for the disease and it's generally found in the liver and the lungs. The liver is the most common location for the disease. No spesific symptoms and signs of HD are present. Generally patients present with unrelated complaints that are related to enlarging cysts. Cysts and microcalcifications within these cysts and varying fluid densities may be found with some imaging modalities such as ultrasound (US), computed tomography (CA) or magnetic resonance imaging (MRI). If the cyst ruptures, severe allergic reactions to parasitic antigens may occur. Clinical history, imaging findings and serological tests should be used in combination for the diagnosis. We present an unusually located pelvic HD in a 24-year-old woman which mimics the bladder. Copyright © 2010 by Türkiye Klinikleri.