Recent national estimates indicate that approximately two-thirds of U.S. high school students do not meet recommended levels of physical activity. (CDC, 2006) Despite the high percentage of U.S. high school students who participate in the labor force (87% of seniors) (Bureau of Labor Statistics, 2005), few studies have examined employment among high school students as a potential barrier or enabling factor for engagement in physical activity. We examined the association between student employment and physical activity among U.S. high school students as measured by overall physical activity, vigorous exercise, and participation in school athletic teams. Secondary analysis of black and white 10th grade (n=12229) and 12th grade students (n=11276) drawn from the nationally representative 2004 Monitoring the Future Study. Students completed self-report questionnaires measuring employment, physical activity, and sociodemographic characteristics. All analyses accounted for the sampling design of the study. Multiple regression analyses were conducted using 3 single-item 5- or 6- point Likert type measures of physical activity as dependent variables and the number of work hours per week as the primary independent variable. All models controlled for gender, race, age, grade average, urban vs. rural residence, and socioeconomic status. Among 10th grade students, 63.5% do not work, 20.6% work ≤10 hours, 10.6% work >10 and ≤ 20 hours, and 5.3% work >20 hours per week. Among 12th grade students, 25.4% do not work, 20.4% work ≤10 hours, 27.4% work >10 and ≤20 hours, and 26.8% work >20 hours per week. Compared to their non-working peers, 10th graders working >10 and ≤20 hours a week reported less exercise (ß= -.452, p<.001) and those working >20 hours reported less participation in athletic teams (ß= -.335, p=.013). 10th grade students working ≤10 hours a week reported more overall physical activity (ß= .131, p<.001) while those working >10 and ≤20 (ß= -.113, p=.014) or >20 (ß= -.293, p<.001) hours a week reported less overall physical activity. 12th graders working >10 and ≤20 hours (ß= -.296, p=.007) and >20 hours (ß= -.543, p=.007) a week reported less overall physical activity. 12th graders working >10 and ≤20 hours (ß= -.465, p=.002) and >20 hours (ß= -.847, p=.007) a week reported less participation in athletic teams; those working >20 hours a week also reported less exercise (ß= -.272 p=.022). Employment at and above 10 hours per week during the school week may have a detrimental effect on physical activity.