The purpose of this study was to examine if steps/day taken by middle school students varied based on aerobic fitness classification. Middle school students (N = 223; 112 girls, 111 boys) were assigned to three aerobic fitness categories (HIGH, MOD, LOW) based on results of the FITNESSGRAM PACER test. Four weekdays of pedometer monitoring determined activity levels (steps/day). Boys accumulated significantly more steps/day than girls, 11,589 plus or minus 3,270 and 10,232 plus or minus 2,517 steps/day, respectively; F(1, 219) = 16.0, p less than 0.001, eta[squared] = 0.055. There were no differences in steps/day between grades. HIGH fit participants accumulated significantly more steps/day, F(2, 217) = 12.2, p less than 0.001, eta[squared] = 0.101, than moderately fit and low fit participants (approximately equal to 1,491 and approximately equal to 2,867 steps/day, respectively). Middle school students who participated in sports in addition to physical education (PE) accumulated significantly more steps/day (approximately equal to 980 steps/day) than those participating in PE only, F(1, 219) = 10.0, p less than 0.01, eta[squared] = 0.044. Although the relationship between physical activity and aerobic fitness was moderate (0.35; p less than 0.01), these data demonstrated significant differences in accumulated steps/day among youth of varying aerobic fitness levels. Whether improved fitness levels were the result of additional activity or the cause of it remains to be determined. Regardless, the fittest middle school students were also the most active and accumulated a significant amount of steps/day through organized extracurricular physical activities. (Contains 2 tables and 2 figures.)