OBJECTIVE: To determine the proportion of male and female research participants and rates of sex-based analysis and sex-specific reporting in published Australian clinical research. PARTICIPANTS AND METHODS: We assessed 400 clinical studies involving Australian-only participants, published in journals between January 1, 2003, and May 31, 2006 (100 per year). Numbers of male and female participants in each study and presence or absence of analysis by sex (covariate adjustment, subgroup analysis, or sex-specific reporting) were recorded. Sex-specific studies were evaluated to determine whether the exclusion of one sex was biologically necessary. RESULTS: The total sample comprised 546,824 participants, of whom 73% were female; 36 studies were male-only, 78 were female-only. Of the participants in 286 studies that were not sex-specific, 56% were female. Of 114 sex-specific studies, the segregation by sex was deemed to be biologically necessary in 62%, ie, the research related directly to male or female biological function. More than one-quarter (28%) of studies with 30 participants or more published covariate adjustment or subgroup analysis by sex; 7% included sex-specific reporting of results. CONCLUSION: We found no routine exclusion of women; however, few publications analyzed results by sex. Some studies excluded women or men for apparently arbitrary reasons. Research performed with male-only participants differed in nature and size from that performed with female-only participants. These data indicate the need to track the sex of research participants. In addition, they provide the basis for assessing appropriate inclusion of men and women in research and for comparing any relationship between different international regulatory models and the rates of female participation in research.