Overall, HIV knowledge increased but was still suboptimal 5 years after baseline. These findings suggest the need to develop and strengthen HIV prevention education programs in youth detention settings. Males had significantly lower HIV knowledge scores than females at baseline only. Over time, Hispanic participants had significantly lower scores than non-Hispanic Black and non-Hispanic White participants. Participants completed an HIV knowledge survey at baseline and up to four more times over 6 years. The authors calculated knowledge scores; the time serial trend of scores was modeled using generalized estimating equations. A baseline survey was completed by 798 participants, ages 14 to 18 years; mean HIV knowledge scores ranged from 11.4 to 14.1 (maximum score = 18). (Publisher abstract modified)