Three versions of a question for establishing the age of respondents were tested in two surveys. All three questions had very low non-response rates; however, asking 'How old are you?' in a mail survey and 'What age range are you in?', together with a drop-down response menu, in an online survey produced significantly higher proportions of incorrectly reported ages. Thus, the best advice for survey researchers is to ask respondents for either their date of birth or the year in which they were born, and to avoid drop-down response menus in online surveys because these can lead to unintended misreporting of answers.