Introduction:: Alternative high school (AHS) students are an underserved population of youth at greater risk for poor health behaviors and outcomes. Little is known about their physical activity patterns. Purpose:: The purpose of this study was to describe 1) physical activity levels of students attending alternative high schools (AHS) in St. Paul/Minneapolis, MN, and 2) compliance with wearing a physical activity accelerometer. Methods:: Sixty-five students (59% male, 65% <18 yr old, 51% African American, 17% Caucasian, 32% mixed and other) wore an accelerometer during all waking hours for 7 d as part of the baseline assessment for a school-based physical activity and dietary behavior intervention. Accelerometer data were reduced to summary variables using a custom software program. Compliance with wearing the accelerometer was assessed by the number of days with ≥10 h of data. Accelerometer counts per minute and minutes spent in moderate-to-vigorous physical activity (MVPA) were calculated. Results:: Students averaged 323 ± 143.0 counts•min and 51 ± 25.5 min•d of MVPA. Minutes of MVPA•d were greater on weekdays compared with the weekend (52 ± 27.3 vs 43 ± 39.7 min•d, respectively; P = 0.05). However, students wore the accelerometer less on the weekends (weekdays = 17.2 ± 3.0, weekend = 14.9 ± 6.8 h•d). Expressing minutes of MVPA as a percentage of the number of minutes of available data, students spent approximately 5% of their time in MVPA on weekdays and weekends. Forty-five percent of students had 7 d of data, 51% had 4-6 d, and 5% had fewer than 4 d. On average, students wore the accelerometer for 17 ± 3.2 h•d (range = 12.0-23.8 h•d). Conclusion:: Compliance was high (95% of students provided at least 4 d of data), and physical activity was relatively low representing a vulnerable population in need of further study and intervention.