Pulmonary hydatid cyst is a common disorder in many areas of the world. In Yemen, echinococcosis is an endemic disease, however, hydatid disease of the lung is uncommon and usually caused by Echinococcus granulosus. We present a case of a 23-year old female who complained of shortness of breath, dry cough and left-sided dull aching pain for the past few weeks. Chest X-ray revealed a large, well-demarcated mass involving the left mid and lower lung zones with mediastinal shift to the right. Computed tomographic scan revealed a giant, low attenuation fluid density mass with enhancing wall. The diagnosis of giant hydatid cyst was confirmed by surgery and histopathological examination. Pulmonary hydatid cyst can assume a very large size without causing any symptoms and can be discovered incidentally while performing chest X-ray for another reason.