There continues to be confusion as to whether papillary adenocarcinoma (PA) of the lung is a specific histologic entity or simply a variant of bronchioloalveolar carcinoma (BAC). We reviewed our files from 1981 through 1993 for all cases (n = 155) of resected primary lung adenocarcinoma specifically diagnosed as having papillary or bronchioloalveolar features. In addition, a random 10% (n = 67) of all remaining lung adenocarcinomas were reviewed. True PA was diagnosed when > or = 75% of the neoplasm contained papillary structures supported by fibrovascular cores with complicated secondary and tertiary branches. Marked nuclear atypia was present in 100%, and psammoma bodies were seen in 42% of cases. In contrast to BAC, true PA filled and distorted or replaced air spaces in the lung. Thirty-one cases of true PA were found, including 19 men and 12 women (mean age, 64.5 years). The lesions were solitary (n = 27) or multifocal (n = 4) with a mean diameter of 4.1 cm. Forty-five percent of patients had bronchopulmonary lymph node involvement at diagnosis; another 10% had extensive intrapulmonary lymphatic permeation by tumor. Disease-free survival for stage I and II PA was 40% (n = 15) and 25% (n = 8), respectively, at a mean of 3.4 and 3.5 years. Papillary adenocarcinoma of the lung is a distinct clinicopathologic entity with considerably worse morbidity and mortality than BAC.