Background: Colorectal cancer is currently the third most common cancer in Indonesia, yet colonoscopy -the most accepted mode of screening to date -is not done routinely and national data are still lacking. Objective: To determine the detection rate of colorectal cancers and adenomas in unselected patients undergoing colonoscopy for various large bowel symptoms at the Digestive Disease and GI Oncology Centre, Medistra Hospital in Jakarta, Indonesia. Materials and Methods: Colonoscopy data from January 2009 to December 2012 were reviewed. New patients referred for colonoscopy were included. Data collected were patient demographic and significant colonoscopy findings such as the presence of hemorrhoids, colonic polyps, colonic diverticula, inflammation, and tumor mass. Histopathological data were obtained for specimens taken by biopsy. Associations between categorical variables were analyzed using chi-square test, while mean differences were tested using the t-test. Results: A total of, 1659 cases were included in this study, 889 (53.6%) of them being men. Polyps or masses were found in 495 (29.8%) patients while malignancy was confirmed in 74 (4.5%). Patients with a polyp or mass were significantly older (60.2 vs 50.8 years; p<0.001; t-test) and their presence was significantly associated with male gender (35.0% vs 23.9%; prevalent ratio [PR] 1.71; 95% confidence interval [CI] 1.38-2.12; p<0.001) and age >50 years (39.6% vs 16.6%; PR 3.29; 95% CI 2.59-4.12; p<0.001). Neoplastic lesions was found in 257 (16.1%), comprising 180 (11.3%) adenomas, 10 (0.6%) in situ carcinomas, and 67 (4.2%) carcinomas. Conclusions: Polyps or masses were found in 30% of colonoscopy patients and malignancies in 16.1%. These figures do not represent the nation-wide demographic status of colorectal cancer, but may reflect a potentially increasing major health problem with colorectal cancer in Indonesia.