The deepest invasive portion of colorectal carcinoma (CRC) is considered to be the part, which ultimately will invade, spread locally and give metastasis. We have previously reported that histologic differentiation at the deepest invasive portion of CRC closely correlate with metastatic potential and is useful in understanding the curability of endoscopic mucosal resection (EMR). The aim of this study is to clarify the conditions of curative EMR for CRC with submucosally (sm) massive invasion. A total of 521 cases with sm invasive CRC (Group A, 470 surgically resected cases; Group B, 51 followed-up cases after EMR) were studied. The depth of sm invasion was defined as the practically measured distance from muscularis mucosae. Histologic subclassification was performed at the deepest invasive tumor margin as: well-differentiated (W), moderately differentiated (M) and poorly differentiated (Por). By assessing glandular configuration and cellular arrangement, M type was further subdivided into two different groups; moderately-well differentiated (Mw) and moderately-poorly differentiated (Mp). In group A, lymph node (LN) metastasis was detected in 45 (9.6%) of 470 cases. W or Mw lesions showed LN metastasis in 4.9% (19/388). Mp or Por lesions showed LN metastasis in 37.3% (25/67) (W/Mw vs Mp/Por; p<0.01). Of 45 cases with LN metastasis that could be measured the practical distance of sm invasion, W or Mw lesions showed no LN metastasis in cases within 1,500 micrometer invasion. However, Mp or Por lesions showed LN metastasis in cases within 1,500 micrometer invasion (5/15, 33.3%, minimum 400 micrometer invasion; so-called scanty invasion). In group B, none of 51 cases died of LN metastasis and showed no other metastasis, although 17 cases (33.3%) showed an sm invasion more than 1,500 micrometer. These results indicated that CRC even with sm massive invasion can be cured by complete EMR on conditions that the depth of sm invasion is within 1,500 micrometer and histologic grade at the deepest invasive portion is W or Mw, if there are no vessel involvement. However, cases with Mp or Por grade were not curative by EMR, even if they showed an sm scanty invasion.