Background: Recent advances of magnifying chromoendoscopy have enabled detailed observation of colorectal neoplasm. According to Kudo's pit pattern classification, we are able to estimate the histology of the lesion, with a high degree of accuracy, without taking biopsies from it. Type I and II are non-neoplastic patterns. Lesions with type IIIs, IIIL and IV are almost always benign adenomas. Type V is seen in cancers. Non-structural pit pattern is called type VN and it represents massively-invasive cancers, requiring surgical treatment. Type VI (I: irregular) reflects structural atypism of cancerous glands, corresponding to wide range of lesions from adenoma to massively-invasive submucosal cancer. Thus it is of great importance to find diagnostic characteristics of deep invasion. Aim: To clarify magnifying endoscopic findings which enable to predict the massive invasion of submucosal cancer exposing type VI pit pattern. Methods: A total of 9255 colonic lesions (including 378 submucosal cancers) were treated at Showa University Northern Yokohama Hospital from April 2001 to June 2008, and classified into seven pit patterns such as type I, II, IIIL, IIIs, IV, VI and VN according to our classification. Of these, 210 submucosal cancers presenting with VI pit pattern were studied. We defined the pit pattern with narrowed lumen, rough margin, unclear boundary, abnormal branching or dense distribution as “type VI-high grade” and evaluated if these findings were useful for predicting the depth of cancer. Endoscopic pictures were judged by endoscopists who were blinded to the final pathological diagnoses. The risk factors of type VI for massive invasion were analyzed according to multiple logistic regressions. Results: Among 210 submucosal cancers with VI pit pattern, 118 (88.7%) of 133 type VI-high grade lesions were massively invasive, whereas 48 (62.4%) of 77 type VI-low grade lesions were slightly invasive. Assuming that type VI-high grade is suggestive of massive invasion, the accuracy, sensitivity and specificity would be 79.1%, 80.3% and 76.2%, respectively. Concerning depressed type lesions, these would be 88.4%, 85.7% and 100%, respectively. Endoscopic findings with narrowed lumen and rough margins were significant risk factors for massive invasion. Conclusion: “Type VI-high grade” is a useful clinical diagnostic finding for determining the depth of invasion in colorectal lesions and their therapeutic selection. Especially in depressed type cancer, this will be an excellent accurate predictor of massive invasion. “Rough margin” and “narrowed lumen” are significant magnifying endoscopic indexes of massively-invasive submucosal cancers.