First admitted in a battered woman's homicide case in 1977, expert testimony on the battered woman syndrome (BWS) is sometimes used to support self-defense claims made by battered women charged with killing their abusers. The aim of expert testimony is to provide the jury with information about the nature of violent relationships and psychological consequences of repeated abuse. Specifically, expert testimony is offered to explain to the judge or the jury how the experience of repeated abuse shapes a battered woman's perceptions and judgments. Questions remain, however, about whether and in what ways expert testimony minimizes blaming the female victim. Some of the work dealing with the use of expert testimony in BWS homicide cases is described. Background information on spousal violence rates is presented, followed by a discussion of gender patterns in homicide, spousal homicide research, and data on battered women who kill their abusive mates. Various legal issues involved in battered women's homicide cases are addressed, including legal dispositions in BWS homicide cases, the admissibility of expert testimony, the content and impact of BWS expert testimony, the relationship between BWS and post-traumatic stress disorder, juror understanding of battering, and experimental research on the impact of BWS expert testimony. The author concludes with a description of recent legislative changes limiting judicial discretion over whether expert testimony is permitted in battered women's criminal cases. 105 references and 11 notes