It is likely that the shift from post- to pre-operative radiotherapy and the introduction of total mesorectal excision (TME) surgery have contributed to the observed improved survival of rectal cancer in the south of the Netherlands. However, no improvement was seen for patients aged 70 or older. To investigate possible causes of this lack of improvement, we examined the risk of treatment-related complications and overall survival. Therefore, a random sample of 455 patients with rectal cancer aged 60 years or older, diagnosed between 1995 and 2001 was extracted from in the Eindhoven Cancer Registry database. Fifty-one percent of patients aged 60-69 years-old had any complication within one year of diagnosis compared to 65% of patients aged 70 or older (p=0.007). Older patients were at higher risk of developing treatment-related complications (odds ratio (OR) 1.8; p=0.01), as were patients with comorbidity (OR 1.7; p=0.07), and those who received pre-operative radiotherapy (OR 1.8; p=0.02). In a multivariable analysis, age older than 70 (hazard ratio (HR) 2.2; p<0.0001), comorbidity (HR 1.7; p=0.03), and having two or more complications (HR=2.2; p=0.0002) had a negative effect on survival. The lack of improvement in the prognosis of elderly patients with rectal cancer after a shift from post- to preoperative radiotherapy might partially be explained by a higher risk of treatment-related complications. In order to optimise the risk/benefit ratio of elderly patients, individualisation of treatment by means of a comprehensive geriatric assessment will be of critical importance.