In 2000, for the first time, men and women aged 16 to 59 were asked details about previous completed cohabitations which did not end in marriage. The number of such cohabitations had previously been asked in 1998. These periods of completed cohabitation did not include the current relationship of respondents who were living as a couple at the time of interview. With the exception of those who chose the self-completion option, the majority of married and cohabiting respondents were interviewed in the presence of their partner; it is therefore possible that, for these groups, there was some under-reporting of previous cohabitations.

Among adults aged 16 to 59 in 2000:

• 14% reported at least one such cohabiting union that did not end in marriage
• 11% had one of these relationships, 2% two and 1% three or more
• there was no difference between the proportions of men and women reporting at least one completed cohabitation not ending in marriage (14% of each did so)
• the highest proportions reporting at least one such relationship were found among men and women aged 25 to 34; almost a quarter of adults aged 30 to 34 reported a previous cohabiting union, compared with, for example, about one in 20 adults aged 50 to 59.