Objective To assess the value of endoscopic miniprobe ultrasonography in the diagnosis of carcinomas and submucosal tumors of the large intestine.Methods A total of 96 patients with carcinomas and submucosal tumors of the large intestine were given colonoscopic ultrasonography with a miniprobe (Olympus UM-2R, 12 MHz; UM-3R, 20 MHz) from December, 2000 to January, 2002. Results Carcinomas of the large intestine of 81 patients appeared as a hypoechoic mass under endoscopic ultrasonography, by which 67 patients (82.7%) were accurately diagnosed as having infiltrated colorectal carcinomas. The sensitivity of endoscopic ultrasonography in the diagnosis of lymph node metastasis was 55.4%, while the specificity was 68.8%. The positive predictive value and the negative predictive value were 0.88 and 0.28, respectively. All 15 cases with submucosal tumors were diagnosed correctly under endoscopic ultrasonography except for one leiomyoma, which was misdiagnosed as leiomyosarcoma. Conclusions Endoscopic miniprobe ultrasonography has a high accuracy in determining the invasion depth of carcinomas of the large intestine and the diagnosis of submucosal tumors. The pre-operative endoscopic ultrasonography may provide valuable information and influence the choice of therapy for carcinomas and submucosal tumors of the large intestine. Objective To assess the value of endoscopic miniprobe ultrasonography in the diagnosis of carcinomas and submucosal tumors of the large intestine. Methods A total of 96 patients with carcinomas and submucosal tumors of the large intestine were given colonoscopic ultrasonography with a miniprobe (Olympus UM-2R, Results 67 cases (82.7%) of patients with accurately diagnosed as having hypoechoic mass under endoscopic ultrasonography, among which 67 patients (82.7%) were accurately diagnosed as having The sensitivity of endoscopic ultrasonography in the diagnosis of lymph node metastasis was 55.4%, while the specificity was 68.8%. The positive predictive value and the negative predictive value were 0.88 and 0.28, respectively. All 15 cases with submucosal tumors were diagnosed correctly under endoscopic ultrasonography except for one leiomyoma, which was misdiagnosed as leiomyosarcoma. Conclusions Endoscopic miniprobe ultrasonography has a high accuracy in determining the invasion depth of carcinomas of the large intestine and the diagnosis of submucosal tumors. The pre-operative endoscopic ultrasonography may provide valuable information and influence the choice of therapy for carcinomas and submucosal tumors of the large intestine .