Background: In patients with stage 1 gastric cancer, surgical resection without neoadjuvant therapy is offered as the first line treatment. However, some of these patients are found to have higher stage after resection and miss the opportunity for neoadjuvant therapy. Preoperative patient and tumor characteristics may be predictive of the likelihood of pathological upstaging in stage 1 gastric cancer patients who have not received neo-adjuvant therapy. Methods: The National Cancer Database was queried for patients diagnosed from 2004-2015 with clinical stage 1 gastric adenocarcinoma who had undergone surgical resection without neoadjuvant therapy. Univariate analysis and multivariable logistic regression were conducted to determine pre-operative factors associated with pathological upstaging. Candidate variables examined included age, sex, race, tumor size, histology, grade, tumor location, days to surgery, and lymphovascular invasion. Results: Analysis was conducted on 8,015 clinical stage 1 patients. Overall 1,981 (25%) patients were upstaged. On multivariable logistic regression analysis, significant predictors of upstaging included increasing tumor size [ref : size < 1 cm, 1-2 cm aOR=3.8 (95% CI 2.3-6.1); 2-4 cm aOR=12.4 (7.9-19.5); > = 4cm aOR=25.9 (22.9-56.4)], younger age [ref: > = 75, < 50 aOR=1.7 (1.4-2.1), 50-65 aOR=1.4 (1.2-1.6), 65-75 aOR=1.2 (1.1-1.5)], male gender [aOR=1.16 (1.0-1.3)], presence of diffuse type gastric cancer [aOR=2.3 (1.7-3.2)], mucinous type [aOR=1.7 (1.1-2.5)], or signet ring cell histology [aOR=1.6 (1.3-2.0)] compared to intestinal histology, presence of lymphovascular invasion [aOR=6.0 (5.0-7.1)], and increasing grade [ref: grade 1, grade 2 aOR=2.30 (1.7-3.5); grade 3 aOR=4.9 (3.6- 6.7)]. Conclusions: A quarter of all patients thought to have stage 1 gastric cancer prior to surgery had higher pathologic stage at time of resection. Patients with the above risk factors may be understaged with currently available diagnostic tools. The addition of neoadjuvant therapy should be considered when the above risk factors are present in clinical stage 1 patients.