Abstract: 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.