Background: A need exists to better understand multilevel influences on physical activity among diverse samples of girls. This study examined correlates of moderate-to-vigorous physical activity (MVPA) among adolescent girls from different racial/ethnic backgrounds. Methods: 1,180 6th grade girls (24.5% black, 15.7% Hispanic, and 59.8% white) completed a supervised self-administered questionnaire that measured hypothesized correlates of PA. MVPA data were collected for 6 days using the ActiGraph accelerometer. Hierarchical regression analysis was used to examine correlates of PA in each racial/ethnic group. Results: Hispanic girls (n = 185) engaged in 21.7 minutes of MVPA per day, black girls (n = 289) engaged in 19.5 minutes of MVPA per day, and white girls (n = 706) engaged in 22.8 minutes of MVPA per day. Perceived transportation barriers (+; P = .010) were significantly and positively related to MVPA for Hispanic girls. For black girls, Body Mass Index (BMI) (–; P = .005) and social support from friends (+; P = .006) were significant correlates of MVPA. For white girls, BMI (–; P < .001), barriers (–; P = .012), social support from friends (+; P = .010), participation in school sports (+; P = .009), and community sports (+; P = .025) were significant correlates of MVPA. Explained variance ranged from 30% to 35%. Conclusions: Correlates of MVPA varied by racial/ethnic groups. Effective interventions in ethnically diverse populations may require culturally tailored strategies.