Aim: The aim of this study was to determine common factors leading to incomplete colonoscopy with a special interest in patient body mass index (BMI), and also to determine most common second line investigation, its pick up rates for cancer and the success rate of re-scoping. Background: Wide availability of scope guide in all procedures may decrease failure rate. Methods: We retrospectively reviewed 2891 colonoscopies performed at our institution from August 2015 to July 2016. The cohort was composed of all incomplete procedures (148) during this time period and a second cohort (148) of complete examinations which were randomly selected for relation of BMI only. The data in incomplete colonoscopy group included age, gender, BMI, causes of failure, mode of referral, second line investigation. The success of re-scope to pick up a cancer was compared to other modalities i. e. CT Colonography etc. Results: Male to female ratio was 1: 4. 8. High incomplete colonoscopy rate was noted in females (81%). Mean age in failure group was 64 ± 15. Average BMI was 28± 15. Most common mode of referral was urgent or suspected cancer (74%). Common cause of failure was patient intolerance (30%). Most common anatomical site of failure was sigmoid colon (35%). Completion rate of re-scoping in experienced hands was 95%. A lower BMI is related with higher chances of failure or vice versa. Conclusion: Lower BMI has higher chance of failure, possibly due to less extra colonic fat leading to tortuous colon. Female sex is second most common cause of failure due to low intolerance to pain. Using stronger pain relief and equal distribution of these characteristics on different list will have least implications in busy cancer screening unit.