Batteries of questions with identical response items are commonly used in survey research. This paper suggests that question order has the potential to cause systematic positive or negative bias on responses to all questions in a battery. Whilst question order effects have been studied for many decades, almost no attention has been given to this topic. The primary aim is to draw attention to this effect, to demonstrate its possible magnitude, and to discuss a range of mechanisms through which it might occur. These include satisficing, anchoring and cooperativeness. The effect seems apparent in the results of a recent survey. This was a survey of Emergency Department patients presenting to Wollongong Hospital (Australia) with apparently less urgent conditions in 2004. Two samples were taken. Question order was fixed in the first sample (n=104; response rate RR2 = 94%), but randomised in the second sample (n=46; response rate RR2 = 96%). Respondents were asked to indicate whether each of 18 reasons for presenting to the ED was a ‘very important reason’, a ‘moderately important reason’, or ‘not a reason’. The mean number of very important reasons selected was 56% higher in the first sample as compared to the second sample.