A 60 percent increase was found in the incidence of sexual assault victims presenting for emergency department (ED) care in 1991 compared to 1974, an increase that was almost entirely explained by an increase in the number of women presenting to the ED after acquaintance rape. Also, a higher rate of reported use of physical force by the assailant and higher rates of bodily trauma for rape victims in 1991 was noted. Lastly, significant changes in treatment practices were also noted with a higher proportion of rape victims receiving pregnancy prophylaxis and empiric antibiotics for sexually transmitted infections in 1991 compared to 1974. Rape and sexual assault are serious problems for women in the United States. An understanding of the epidemiology of sexual assault may be helpful to the medical professionals who treat rape victims and public health officials who develop prevention programs. Women who seek medical care following sexual assault are usually evaluated and treated in the ED. EDs can be an important source of sexual assault surveillance data. The data can be used to identify temporal and demographic trends in sexual assault. This study compared the incidence of sexual assault presenting for emergency care in a single county during July to November of 1974 and 1991. Participants included all female sexual assault victims aged 14 and older who presented for ED evaluation. Figure, table, and references