Objectives: To compare the characteristics of sexual assault in pubertal girls (<18 years old) and adults in a community-based population of women presenting to an urban sexual assault clinic. Methods: This case-series analysis evaluated consecutive female patients presenting to a sexual assault clinic during a three-year study period. The clinic is associated with a university-affiliated emergency medicine residency program and is staffed by forensic nurses trained to perform medicolegal examinations using colposcopy with nuclear staining. Patient demographics, assault characteristics, and injury patterns were recorded using a standardized classification system. Data from the two patient groups (adolescents vs. women ≥18 years of age) were analyzed using chi-square test and t-test. Results: A total of 766 cases were identified: 43% of the victims were 13 to 17 years old (mean 15.0 years old), and 57% were older than 17 years old (mean 30.8 years old). Adolescents were more likely to be assaulted by an acquaintance or relative (84% vs. 50%, p < 0.001) and to delay medical evaluation (17 hours vs. 12 hours, p < 0.001) than were older women. Adolescent sexual assault was less likely to involve weapons or physical coercion (29% versus 57%, p < 0.001) and was associated with fewer nongenital injuries (33% vs. 55%, p < 0.001). Adolescents had a greater frequency of anogenital injuries (83% vs. 64%, p < 0.001), however, compared with older women. Common sites of injury in adolescents were posterior, including the fossa navicularis, hymen, fourchette, and labia minora. The injuries showed consistent topologic features, varying with the site and nature of tissue. Adult victims of sexual assault had a less consistent pattern of anogenital injuries with fewer hymenal injuries, greater injury to the perianal area, and widespread erythema. Conclusions: Of women presenting to an urban sexual assault clinic, 43% were adolescents. The epidemiology of sexual trauma and the pattern of anogenital trauma in this age group are unique and may pose special challenges to emergency health care providers.