Echinococcus granulosus, the pathogen responsible for hydatid disease, mostly settles in the liver and lungs but affects the peritoneum less frequently. Rupture of a cyst into the peritoneal cavity is a potentially life-threatening incident. Although numerous studies on ruptured hepatic hydatid cysts have been published, few cases of peritoneal cyst rupture have been reported. We describe the case of a 19-year-old woman who presented with an acute abdomen and allergic reactions after a fall. Ultrasonography and computed tomography revealed a hydatid cyst of the liver and ruptured pelvic hydatid cyst. First, the patient received appropriate measures to prevent anaphylactic shock and later underwent emergency surgery. Partial cystectomy of the ruptured pelvic hydatid cyst, peritoneal washing, and unroofing of the large unruptured hepatic hydatid cyst were conducted. Albendazole was administered postoperatively for 3 months. No recurrence was noticed during 3 years of follow-up. Although rarely documented, acute rupture of a peritoneal hydatid cyst is the most severe complication of peritoneal echinococcosis. Typically after trauma, it must be considered in the presence of an acute abdomen with allergic reactions. Ultrasonography and computed tomography have high sensitivity in demonstrating rupture of a hydatid cyst. Emergency surgery is the only effective treatment and should aim at the complete removal of a cyst, if possible, and peritoneal washing with scolicidal agents. Additional studies should be conducted to evaluate the feasibility of laparoscopy. Albendazole should be prescribed postoperatively to prevent recurrence. Mortality is closely related to anaphylaxis; hence, early and accurate diagnosis and appropriate preventive measures are crucial.