Data on the likelihood of Mycoplasma genitalium infection in sexual contacts, particularly for men who have sex with men (MSM), are needed to form an evidence base for guidelines. We conducted a cross-sectional analysis of patients attending a sexual health clinic in Melbourne, Victoria, Australia, during 2008-2016. We calculated the proportion of contacts with M. genitalium infection and determined factors associated with infection. Among those patients reporting sexual contact with an M. genitalium-infected person, 48.2% of women, 31.0% of heterosexual men, and 41.7% of MSM were infected. Among heterosexual contacts, women were twice as likely to be infected; among MSM, rectal infection was more common than urethral infection; and among persons in heterosexual partnerships, concordance of infection was high. High positivity among female and MSM contacts and high concordance within heterosexual partnerships provide some justification for presumptive treatment; however, clinicians should consider antimicrobial drug resistance and toxicity of quinolones.