A new study strengthens growing evidence that Mycoplasma genitalium (MG) is a sexually transmitted infection (STI). Prevalence was much higher in those who had reported more than four sexual partners in the past year — 5.2% in men and 3.1% in women. Absence of the infection in over 200 16-17 year olds who had not had vaginal, anal, or oral sex provided further evidence that MG is transmitted sexually.