Background: With the emergence of improved treatment strategies for patients with malignant lung tumors, it has become increasingly important to adequately diagnose and subclassify lung lesions. In our large retrospective study, we assessed the utility of fine-needle aspiration (FNA) in the diagnosis of primary and metastatic tumors to the lung. Methods: A computerized search of our laboratory informatics system was performed to identify cases from FNA of the lung and FNA of metastatic lung cancers to other sites. All of the corresponding surgical pathology reports were also reviewed. All of the cases were categorized as atypical (A), benign (B), malignant (M), nondiagnostic (ND), or suspicious (S) for data analysis purposes. Results: A total of 1,032 FNA cases were categorized as follows: 34 (3.3%) A, 142 (13.8%) B, 717 (69.5%) M, 121 (11.7%) ND, and 18 (1.7%) S. Of the 717 cases of malignant FNA, a specific tumor type was able to be rendered on cytomorphology alone or with the help of immunostains in 99% as follows: adenocarcinoma (296 cases, 41%), squamous cell carcinoma (158 cases, 22%), metastatic tumors (123 cases, 17%), small cell carcinoma (56 cases, 8%), non-small cell lung carcinoma (NSCLC) (58 cases, 8%), neuroendocrine carcinoma (15 cases, 2%), and poorly differentiated carcinoma (4 cases, 1%). Out of all NSCLC cases, 89% were able to be subclassified as either adenocarcinoma or squamous carcinoma. The most frequent origins of metastatic tumors to the lung were renal cell carcinoma (n = 22), melanoma (n = 17), colon (n = 15), breast (n = 14), and urothelial carcinoma (n = 10). There was also metastasis from 18 other organs with fewer than 5 cases each. There were 333 correlated histologic specimens including 191 small biopsies and 142 resection specimens. Diagnostic sensitivity and specificity for malignancy were 96 and 100%, respectively. Diagnostic accuracy was 97%. Sampling error resulted in 8 false-negative cases on FNA. Conclusions: FNA is both sensitive and specific in the diagnosis and subclassification of both primary and metastatic lung tumors. Eighty-nine percent of NSCLC cases were able to be further subclassified as adenocarcinoma or squamous cell carcinoma by FNA.