Colonoscopy is the main investigation to detect the abnormalities in the colon and it is the main supportive measure for clinical diagnosis. Colonoscopic biopsy helps to get a definitive diagnosis of colonic diseases, which helps the clinician to give appropriate treatment. Aim of the Study: To know the pattern of colonic diseases by colonoscopy and histopathological examination in Chennai Medical College Hospital __ampersandsignamp; Research centre (CMCH__ampersandsignamp;RC) Irungalur Thiruchirapalli District. a tertiary care hospital in rural part of south India. Materials and Methods: A retrospective study of patients who had undergone colonoscopy from November 2014 to December 2017 at CMCH__ampersandsignamp;RC was done. Data, from endoscopy register __ampersandsignamp; from histopathology register during that period were collected and analysed. Results: A total of 919 patients registered for colonoscopy. Male: Female ratio was 614:305.913 patients tolerated the procedure. The most common indications were bleeding per rectum 208 cases (22.78%), clinical suspicion of irritable bowel syndrome 151 cases (16.54%), constipation 115 cases (12.60%), abdominal pain 62 cases (6.79%). The colonscopic findings were, normal study in 47.65%, hemorrhoids in 17.42%, polyps in 8.65%, carcinoma in 6.68%, inflammatory bowel disease in 7.56% of case. About 137 biopsy taken by colonoscopy during this period. The results were malignant lesions in 52, non specific colitis in 27 , benign neoplastic lesions in 14, ulcerative colitis were 13 cases. Conclusion: The commonest lesion by colonoscopy was hemorrhoids, Histopathological examination supports the colonoscopic study. Commonest lesion by histopathology was malignancy. The increasing incidence of malignancy in younger age group needs further prospective study.