Incapacitated/drug-alcohol facilitated sexual assault (IS/DAFS) is rapidly gaining recognition as a distinct form of assault with unique public health implications. This study reports the prevalence, case characteristics, and associated health risks of IS/DAFS using a large, nationally representative sample of 1,763 adolescent girls. Results indicate that 11.8% of girls experienced at least one form of sexual assault; 2.1% of the total sample experienced IS/DAFS. Thus IS/DAFS accounted for 18% of all reported sexual assaults, with a prevalence of 4.0% among girls 15 to 17 years of age and 0.7% among girls 12 to 14 years of age. Girls with a history of IS/DAFS were significantly more likely than girls with other sexual assault histories to report past-year substance abuse but not significantly more likely than girls with other sexual assault histories to report past-year depression or posttraumatic stress disorder. (Contains 1 table and 1 figure.)