In order to examine factors associated with orgasm in heterosexual encounters, we analyzed data from the Australian Study of Health and Relationships, a national telephone survey of sexual behavior and attitudes and sexual health knowledge carried out in 2001-2002 with a representative sample of 19,307 Australians aged 16 to 59. Respondents were asked whether at their last sexual encounter they gave or received manual stimulation and oral sex, had vaginal intercourse or anal intercourse, and whether they had an orgasm. Vaginal intercourse was the dominant practice: 95% of encounters included it. Of the 64 possible combinations of these practices, 13 account for 93% of encounters: vaginal intercourse alone (12%), vaginal + manual stimulation of the man's and/or woman's genitals (49%), and vaginal intercourse + manual + oral (32%). Encounters may also have included other practices. Men had an orgasm in 95% of encounters and women in 69%. Generally, the more practices engaged in, the higher a woman's chance of having an orgasm. Women were more likely to reach orgasm in encounters including cunnilingus. This is the first large-scale empirical study worldwide to link specific practices with orgasm. Demographic and sexual history variables were comparatively weakly associated with orgasm.