Background The concept of concurrent partnerships, while theoretically appealing, has been challenged at many levels. However, non-monogamy may be an important risk factor for the acquisition and transmission of sexually transmitted infections (STI). One's own non-monogamy is a risk factor for transmitting STI to others, partners' non-monogamy is a risk factor for acquiring STI and, most importantly, mutual non-monogamy is a population level determinant of increased STI spread. This study describes the levels, distribution and correlates of non-monogamy, partners' non-monogamy and mutual non-monogamy among adult men and women in the USA.

Methods Data from the National Survey of Family Growth (NSFG) Cycle 6 were used. NSFG is a national household survey of subjects aged 15–44 years in the USA. Cochran–Mantel–Haenszel tests and χ² tests were used in the analysis.

Results Among sexually active adults, 17.6% of women and 23.0% of men (an estimated 19 million) reported non-monogamy over the past 12 months in 2002. An estimated 11 million Americans (1 in 10) reported partners' non-monogamy and an estimated 8.4 million (7% of women and 10.5% of men) reported mutual non-monogamy. All three types of non-monogamy were reported more frequently by men than women. Younger age, lower education, formerly or never married status, living below the poverty level and having spent time in jail were associated with all three types of non-monogamy in general.

Conclusions The three types of non-monogamy may be helpful in tailoring prevention messages and targeting prevention efforts to subgroups most likely to spread infection.