Anastomotic dehiscence is a serious, life-threatening complication of any rectal anastomosis and may be associated with an increased risk of local cancer recurrence. The leak rate following low anterior resection is in the region of 10% as supported by the recent randomised Dutch rectal cancer trial. Although accurate prediction of risk is impossible, certain factors are known to influence leak rates. There is an inverse relationship between the height of anastomoses from the anal verge and leak rate, with the lower anastomoses carrying the highest risk. Proximal defunctioning mitigates the consequences of leakage but does not abolish risk. There is little difference in rates of dehiscence between stapled and sutured colorectal anastomoses. A short colon pouch may reduce the chance of leakage. The highest risks are in unprotected anastomoses less than 5 cm from the anal verge in men who smoke and/or drink excessively, particularly if they have received pre-operative chemotherapy or chemo-radiotherapy. A high index of suspicion is required in detecting the early nonspecific signs of a leak and urgent surgical intervention is usually required to avert a life-threatening situation. Judicious use of faecal diversion should never be regarded as surgical timidity.