Hydatid cyst is a disease caused by a parasitic tapeworm, Echinococcus granulosus, and most commonly involves liver and lung. Ruptured pulmonary hydatid cyst can present a diagnostic challenge, and radiograph can be inconclusive. Anaphylactic reaction is a rare complication of ruptured pulmonary hydatid cyst. A 22-year-old male came to our emergency department in shock with symptoms of shortness of breath and altered mental status from the previous day. Radiograph showed a thin-walled circular translucent area in the right upper lung field, which was misdiagnosed as pneumothorax, and an intercostal chest tube was inserted. After 5 days, repeat radiograph revealed a cavity with an air/fluid level. The chest tube was removed and contrast-enhanced computed tomogram showed a cavity with water-lily sign, which suggests ruptured hydatid cyst. Immunoglobin-G enzyme-linked immunosorbent assay for Echinococcus was positive. The patient responded well to treatment with crystalloid infusion, supplemental oxygen, and albendazole, and then underwent surgery. Anaphylactic reaction due to rupture of a hydatid cyst is rare, but hydatid disease should be suspected in patients from areas where Echinococcus is endemic.