Background <p>The prognosis of non-curative endoscopic submucosal dissection (ESD) for undifferentiated-type early gastric cancer (UD-EGC) remains unclear. This study aimed to identify risk factors for residual tumor, lymph node metastasis (LNM), and recurrence after non-curative ESD, and to define a potential low-risk subgroup suitable for active surveillance rather than additional surgery.</p> Methods <p>This retrospective multicenter study included patients with non-curative ESD for UD-EGC from five institutions between 2017 and 2021. Patients were categorized into an additional surgery group or an observation group according to subsequent management. Clinicopathologic characteristics and survival outcomes were compared.</p> Results <p>Ninety-nine patients were analyzed, including 44 in the observation group and 55 in the additional surgery group. The median follow-up duration was 64&#xa0;months. Six patients undergoing surveillance experienced recurrence within 12.0 to 37.3&#xa0;months after ESD. Fourteen patients in the additional surgery group showed residual tumor or LNM. Vertical margin involvement independently predicted recurrence in the observation group, while ulceration and vertical margin involvement were independent predictors of residual tumor or LNM in surgical specimens or recurrence. Overall and disease-free survival were worse in the observation group. Disease-free survival in the observation group was associated with depth of invasion, lymphatic invasion, venous invasion, and resection margin status. Lesions with negative resection margins and no lymphovascular invasion meeting either (1) pT1a, UL0, &gt; 2&#xa0;cm, or (2) pT1a, UL1, ≤ 3&#xa0;cm demonstrated excellent long-term outcomes without recurrence.</p> Conclusions <p>Additional surgery remains standard after non-curative ESD for UD-EGC. However, a carefully selected low-risk subgroup may be appropriate candidates for close surveillance instead of further surgical intervention.</p> Graphical abstract <p></p>