Research on sexual homicide is problematic because it is not defined by statute, and the Diagnostic and Statistical Manual of Mental Disorders has never defined sexual homicide as a paraphilia. In addition there are clear distinctions among a sexual murder, in which the killing itself is sexually arousing; a murder committed in order to cover up a sexual crime; and a homicide that has some sexual component, but has unclear motivation. In addition to definitional and crime-incidence complexities in research on sexual homicide, there are several practical obstacles to research in this area. First, sexual homicide is a rare event. Second, unlike sexual offenders, sexual murderers are not labeled as such either legally or institutionally. This makes it difficult to identify them for research purposes. Third, when a sexual murderer is evaluated, his background, which is important for understanding motivational dynamics, is often incomplete and inaccurate because of various legal restriction as well as personal motives to lie, exaggerate, and distort. Fourth, for years mental health professionals have worked independently of other professionals (e.g., criminal investigators) who have a wealth of information on sexual homicide, but from a different (crime scene analysis) perspective. The discussion of catathymic and compulsive sexual homicides is sometimes problematic. Both types of sexual murder have a basis in underlying sexual conflict; however, the nature of the sexual conflict differs. Catathymic homicides are typically single explosions triggered by some type of challenge to the individual's sense of sexual competence. Compulsive sexual homicides stem from a longstanding and developing urge to kill, which itself is eroticized. Implications are drawn for the treatment and prevention of these two types of sexual homicide. 80 references