Pulmonary invasive mucinous adenocarcinoma (PIMA) formerly known as mucinous bronchioalveolar carcinoma is a relatively rare variant of pulmonary adenocarcinoma, but the incidence of this tumor is known to be rising. Imaging findings may include nodules, masses and lobar involvement of variable densities, but the majority present as air-space consolidation. We report a case of PIMA with radiological-pathological correlation in a 23-year-old male which presented as a large cavitary mass mimicking congenital cystic lung disease.gans