Colorectal cancer is the third most frequent illness of all carcinomas with an increase in the incidence of colorectal cancer in highly developed countries. 75% of patients with colorectal cancer are older than 65 years. It is believed that 66-75% of colorectal cancer could be avoided through healthy lifestyle. 75% of colorectal cancer arise from adenomatous polyp but more than 90% of adenomas will not progress to carcinoma. Colonoscopy has become the preferred method for evaluation of lower digestive symptoms and detection and treatment of colon pathology, and is considered to be the gold standard for colorectal cancer screening and surveillance. Aim of this paper is to resolve some dilemmas and answer the most frequently asked questions from primary care physicians about colonoscopy such as indications, contraindications, the role of colonoscopy in colorectal cancer screening, how often colonoscopy should be repeated, why it is so important to prepare colon and patients for colonoscopy and what type of complications can happen.