Little about primary tumor size and nodal/distant metastases among different cell types in non-small cell lung cancer (NSCLC) was discussed. This study aimed to investigate distinct associations between tumor size and nodal/distant metastases in pulmonary adenocarcinoma and squamous cell carcinoma. The study also aimed to clarify the cutoff size relating to a higher likelihood of metastases. We retrospectively evaluated 932 NSCLC patients over a 3-year period and focused on cases with primary tumors less than 4.0 cm in size. Our data showed that 2.5 cm was the critical cutoff size regarding increased nodal/distant metastases in adenocarcinoma (p<0.001), but not in squamous cell carcinoma (p>0.05). In addition, the incidence of nodal/distant metastases reached a plateau of more than 80% in adenocarcinoma when the tumor size exceeded 2.5 cm. In contrast, there was no such correlation observed in squamous cell carcinoma. This study showed that tumor size mattered differently in pulmonary adenocarcinoma and squamous cell carcinoma.