As more attention is directed to the mental health care of women, sex and gender differences in research design and in regulatory policies have interfaced with clinical care and public policy. An emphasis on women's mental health issues in the provision of treatment and care as well as the design of large-scale screening strategies to identify and treat women with mental disorders promises to be effective public health approaches to reducing the burden of mental illness in women. The past decade has seen increased emphasis on women's mental health and sex/gender differences in the federal sector and in the research community. Federal regulations (summarized in the NIH Outreach Notebook) call for the inclusion of women and minorities in NIH-funded clinical research. The regulations also place emphasis on gender analysis of the results of clinical trials, in particular phase III trials, the findings of which are likely to influence practice. There has been substantial progress toward the goal of including women in research, but more remains to be done. A 2000 GAO report titled "Women's Health: NIH Has Increased Its Efforts to Include Women in Research" commended NIH for tracking the number of women in clinical research but the report also noted that relatively few NIH-funded studies, including major clinical trials, had reported findings by gender of study participants. This was seen as an impediment to progress in developing gender-based effective treatments. In the past decade, the women's health field has moved beyond an exclusive emphasis on women's reproductive function to one that defines health as a scientific enterprise to identify clinically important sex and gender differences in prevalence, etiology, course, and treatment of illnesses affecting men and women in the population as well as conditions specific to women. Nonetheless, for mental disorders, women's reproductive function and its impact on mental health conditions is still understudied. Based on the epidemiology of mental disorders, the course of mental disorders in women in relation to reproductive transitions remains an important issue for the mental health field because the burden of mental disorders, such as depression and anxiety, fall disproportionately on women of childbearing and childrearing age. The public health emphasis on women's mental health does not lessen the basic scientific opportunities to be had by a focus on gender and sex differences. A 2001 report of the Institute of Medicine titled "Exploring the Biological Contributions to Health: Does Sex Matter?" underscores the benefit to health care of looking for sex differences at the biological level. Basic and clinical neuroscience research is rapidly accruing a knowledge base that will provide information at the level of genes and cells of the influences of biological sex on mental health outcomes in both women and men. A focus on women's mental health and gender/sex differences research promises to yield improvement in treatments and services and thereby to improve the public health as well as to increase fundamental knowledge about the etiology and neurophysiology of mental disorders.