BACKGROUND: Although the incidence of cervical dysplasia in adolescents is increasing, a paucity of data exists regarding the outcomes of adolescents with Pap test abnormalities. We determined the natural history and outcome of adolescents with low-grade squamous intraepithelial lesions (LSIL) and high-grade squamous intraepithelial lesions (HSIL). METHODS: A review of all women aged 18 years or younger with a cytologic diagnosis of LSIL or HSIL between 1997 and 2003 was performed. Follow-up cytologic and histologic samples were evaluated. The most significant abnormality was recorded for each patient. Rates of regression, persistence, and progression were calculated. RESULTS: A total of 646 adolescents were identified. Follow-up was available for 477 teenagers with LSIL and for 55 with HSIL. Among adolescents with LSIL, 146 (35%) had negative follow-up. Low-grade abnormalities (atypical squamous cells of undetermined significance, LSIL, and cervical intraepithelial neoplasia grade 1) were seen in 199 (47%), whereas high-grade abnormalities were documented in 77 (18%). After 36 months, 62% had regressed, whereas 31% had progressive dysplasia. For the HSIL cohort, negative follow-up was documented in 12 (21.8%) adolescents, and 15 (27.3%) had low-grade abnormalities, whereas more than one half (50.9%) were found to have a high-grade abnormality. At 36 months, 31% of HSIL subjects had progressed to cervical intraepithelial neoplasia 3. CONCLUSION: Adolescents with LSIL and HSIL cytology are at significant risk for progression to high-grade cervical abnormalities. The rate of development of high-grade cervical abnormalities in adolescents is similar to adults. Adolescents with cytologic abnormalities mandate close follow-up. LEVEL OF EVIDENCE: II-3.