Background: To evaluate the risk of recurrence in patients with pathologically staged Ib, according to the American Joint Committee on Cancer (AJCC) 2002 staging system, gastric cancer (GC) in the phase III adjuvant chemoradiotherapy in stomach tumors (ARTIST) trial. Methods: Among 458 GC patients enrolled in ARTIST, 99 had stage Ib (T2N0 or T1N1) disease. Patients were randomly assigned to receive adjuvant chemoradiotherapy with capecitabine plus cisplatin (XP, n = 50)) or chemoradiotherapy (XPRT, n = 49). Kaplan-Meier method was used to calculate disease-free survival (DFS). Cox proportional hazard models were employed to determine associations between the addition of radiotherapy to XP and DFS after adjustment for patient and disease characteristics. Additionally, analyses were performed according to the AJCC 2010 staging system. Results: With 7 years of follow-up, there were 18 recurrences. The 5-year DFS rates were 88% and 84% in XP and XPRT patients, respectively (P = 0.537). When we reviewed the pathologic stages of the patients according to the AJCC 2010 system, stage migration from Ib to II occurred in 71% of the patients: 98% of the T2N0 patients were reclassified as T3N0, and 42% of the T1N1 patients were reclassified as T1N2. The patients classified as stage Ib according to the AJCC 2002 system and reclassified as stage II exhibited worse, although statistically insignificant, prognosis than the patients who remained in stage Ib (5-year DFS 83% vs. 93%, P = 0.183, HR 1.178, 95% CI 0.420-3.311, P = 0.158). When we compared 5-year DFS in 70 stage II (AJCC 2010 system) patients, the addition of radiotherapy to XP chemotherapy resulted, although again statistically insignificant (P = 0.234), in worse outcome in XPRT arm (77%) than in XPRT arm (88%). Conclusions: This subgroup analysis confirms the clinical relevance of the AJCC 2010 staging system in GC. The role of adjuvant chemotherapy in stage II GC warrants further investigation.