According to experience in a self-payed health check-up center,unsedated total colonoscopy is not inferior or may be better than unsedated sigmoidoscopy in terms of pain and patients' acceptance.

Hypothesis: Unsedated total colonoscopy is not inferior to unsedated sigmoidoscopy in terms of pain and patients' acceptance.

According to American Cancer Society guideline, screening total colonoscopy every 10 years or sigmoidoscopy every 5 years is recommended for average risk people above 50 years old. However,study in Taiwanese population demonstrated that 37.8% of colorectal lesions were beyond reach of sigmoidoscope, and in cases with lesions with advanced pathology, 66.7% did not have distal colorectal lesion. However, many people think colonoscopy is more painful and choose sigmoidoscopy for screening. However, according to experience in a self-payed health check-up center,unsedated total colonoscopy is not inferior or may be better than unsedated sigmoidoscopy in terms of pain and patients' acceptance.

Inclusion Criteria:

• Subjects who undergo self-payed unsedated colonoscopy or sigmoidoscopy for colon cancer screening.

Exclusion Criteria:

• Difficulty in assessing pain during the procedure and acceptance for the procedure