RESULTS: Of 27642 newly diagnosed lung cancer patients, 283 patients (1.02%) harboring additional primaries. Compared with single primary lung cancer, patients with multiple primaries were more often women (female to male ratio of 1:1.72 vs 1:2.59, P=0.018) and older (64.2 vs 60.5 years, P<0.001), more squamous cell type (30.7% vs 20.7%, P=0.004) and less small cell (3.9% vs 20.7%, P<0.001) type, present at earlier stages (17.7% vs 10.9% for stage I, P=0.014), and more frequently have a family history of cancer (7.8% vs 3.9%, P=0.038). The most common primaries observed were cancers of colorectal (22.0%), breast (18.4%), gastric (14.4%) and larynx (11.9%). Approximately 42.9% of lung cancers were found 2 to 6 years after initial primaries. The survival of patients with multiple primary malignancies associated lung cancer is not significantly different from those with single lung cancer diagnosis (P=0.491), while synchronous multiple primary malignancies have obviously worse prognosis than those with metachronous or single ones (p=0.012).