Homeless women are a large and diverse group, constituting one fifth of the US homeless adult population. Although most homeless women do not have major mental illness, homeless women exhibit disproportionately high rates of major mental disorders and other mental problems. Rates of mental disorders are highest among whites and women without children, and important variations by subgroups of homeless women reinforce the need for disaggregated analysis. Many homeless women with serious mental illness are not receiving needed care, apparently due in part to the lack of perception of a mental health problem and the lack of services designed to meet the special needs of homeless women.