Purpose: To describe baseline prevalence of oral mucosal diseases among HIV infected adolescents in relationship to biological and behavioral risk factors. Methods: Participants in Reaching for Excellence in Adolescent Care and Health (REACH), a multicenter longitudinal observational study of HIV/AIDS in adolescents, received physical examinations, blood tests, and oral examinations at 3-month intervals. We evaluated participants for oral conditions commonly seen in relationship to HIV, and explored the association of the most common lesion with selected biological and behavioral variables at baseline using contingency tables and Fisher's Exact test. Results: Among 294 HIV infected adolescents recruited between March 1996 and March 1999, the majority were female (75%), aged 17 to 18 years (69%), and African-American (73%). More than 90% had a CD4 + T-lymphocyte count > 200 cells/mm 3 at baseline and 57% had a plasma HIV-1 RNA concentration ≤5000 copies/mL. The most common condition was oral candidiasis (6%), predominantly the pseudomembranous type. The only variable found to be associated with oral candidiasis was elevated plasma HIV-1 RNA concentration (p = .03). Aside from 2 cases of hairy leukoplakia and aphthous ulcers, no other oral mucosal lesions were identified in this subject population with apparently early HIV disease. Conclusion: Similar types of oral lesions were observed in HIV infected adolescents as have been seen in adults, although the prevalence of these lesions was low. Elevated plasma HIV-1 RNA concentration was found to be associated with the baseline prevalence of oral candidiasis, and appeared to be a better predictor of HIV-related oral disease than CD4 + T cell count in this cohort at early stage of HIV disease. Copyright © 2001 Society for Adolescent Medicine.