Introduction The term ‘fuckbuddy’ has been widely used in the men who have sex with men (MSM) population; however, this term is often classified as either ‘regular’ or ‘casual’ partnerships in sexual health research. We aimed to examine the definition of ‘fuckbuddy’ in MSM population and to assess the risk factors for having a fuckbuddy.

Methods We conducted a mixed method study among MSM at the Melbourne Sexual Health Centre, Australia, between March and September 2015. (1) MSM attending MSHC during the study period were invited to complete a questionnaire about their regular and casual partnerships in the last three months. (2) Semi-structured interviews were conducted with 30 MSM who were asked their views on the terminology they used to describe their relationships and sexual partners.

Results A total of 939 MSM completed the questionnaire and 502 MSM had at least one regular partner, with a total of 1139 regular partnerships reported. The majority of regular partners were classified as ‘fuckbuddies’ (60% [95% CI 57%–63%], 686/1139) s’, followed by ‘partners’ (16% [95% CI 14%–18%]) and ‘boyfriends’ (16% [95% CI 14%–18%]). MSM who had at least one ‘fuckbuddy’ were 2.4 (95% CI 1.29, 4.41) times more likely to acquire rectal chlamydia after adjusting for total number of partners and condom use. Findings from interviews showed that the there was a consensus among men that partners they engaged with for ‘sex only’ were classified as casual partners, and partners with whom there was an emotional attachment or formalisation of the relationship, were classified as ‘regular partners’. However, the classification of ‘fuckbuddy’ as a regular or casual partner was less clear.

Conclusion MSM with ‘fuckbuddies’ are at greater risk of acquiring STIs such as rectal chlamydia. Further research is needed to ascertain the ways in which men conceptualise sexual relationships and define or classify partner types, particularly ‘fuckbuddy’ relationships. A third category for sexual relationships should be considered to encapsulate fuckbuddy relationships.