Aim: Surgical resection is a standard therapeutic approach for some cases of non-small cell lung cancer (NSCLC). Fluorodeoxyglucose positron-emission tomography (FDG-PET) is now widely used in clinical diagnosis and staging of various types of cancers, including NSCLC. We investigated whether the maximum standardized uptake value (SUVmax) of primary tumors is useful in predicting the extent of lymph node involvement. Patients and Methods: We retrospectively evaluated 354 patients with NSCLC who underwent surgery following FDG-PET and computed tomographic (CT) scans in our hospital. Logistic regression analyses were used to assess associations between categories (age, sex, tumor size, SUVmax, serum Squamous cell carcinoma-related antigen (SCC), cytokeratin 19 fragment (CYFRA), carcinoembryonic antigen (CEA), Brinkman index and histologic type. Differences in SUVmax of primary tumors between positive and negative lymph node involvement were examined by Mann Whitney U-test. Results: SUVmax of primary tumors in patients without lymph node involvement was significantly lower than in those with involvement, in both adenocarcinoma and squamous cell carcinomas (median, 2.2 vs. 4.9 in adenocarcinoma and 5.0 vs. 8.1 in squamous cell carcinoma, p<0.001 for both). Among node-positive cases, the lowest primary tumor SUVmax. was 1.24 in an adenocarcinoma and 2.05 in a squamous cell carcinoma. However, primary tumor SUVmax, and extent of lymph node metastases showed no significant differences between pN1 and pN2, single and multiple lymph node involvement, or single and multiple station involvement. Conclusion: A low primary tumor SUVmax in NSCLC may help identify patients with no lymph node involvement. However, SUVmax does not discriminate between minimal and extended lymph node involvement.