Multiple primary carcinomas of lung

12 cases of multiple primary carcinomas of the lung out of 745 patients with lung cancers operated, confirmed by pathologic examination, are reported, the incidence being 1.6%. The pathologic associations of lesions are squamous carcinoma and squamous carcinoma in 4 cases, squamous carcinoma and small-cell carcinoma in 3, squamous carcinoma and adenocarcinoma in 1, undifferentiated carcinoma and giant-cell carcinoma in 1, bronchiolo-alveolar carcinoma and bronchiolo-alveolar carcinoma in 1 and adenocarcinoma and adenocarcinoma in another. In 1 casc. The threefold primary carcinomas are all adenocarcinoma the cause of the increase in incidence, clinical characters, diagnosis, differential diagnosis and surgical treetment are discussed.