While calorimetry, direct observation, and doubly-labeled water (DLW) are often considered the most valid means of assessing physical activity, electronic devices, including heart rate and activity sensor monitors, hold great promise for objectively and conveniently collecting continual activity information at the lowest cost in free-living individuals. Accelerometers, in particular, can measure quantity and intensity of physical activity. PURPOSES: To compare: 1) reproducibility of accelerometer measures between two similarly structured metabolic camp sessions for overweight/obese adolescents; 2) data derived from accelerometers worn on the wrist and the hip; and 3) two regression models (single regression [1R] and double regression [2R], which is intended to accommodate low activity better than [1R]), provided with the manufacturer software. METHODS: Fifteen boys (mean ± SD: 13.8 ± 0.7 yrs, body fat % = 36.6 ± 9.2) and 21 girls (13.5 ± 0.8 yrs, body fat % = 45 ± 4.7) wore accelerometers on the non-dominant wrist during the first session (S1) of the camp, and on both the wrist and right hip during session two (S2) for 17 consecutive 24-h days each session. Independent and paired t-tests, and Pearson r correlations were used for analysis. RESULTS: There were no differences between S1 and S2 wrist activity counts/min (AC) for either boys (P = 0.92) or girls (P = 0.56). Although S2 wrist AC were higher (P = 0.0001) than hip AC for both boys (wrist = 833 ± 161; hip = 361± 52) and girls (wrist= 704 ± 200; hip= 300 ± 63), they were correlated (r = 0.95, P = 0.0001) in both genders. Boys had higher AC counts at both sites (wrist S1: P = 0.006; S2: P= 0.016 and hip S2: (P = 0.001) compared to the girls. No difference between 1R and 2R means was observed on the wrist (boys: P = 0. 62; girls: P = 0.54). 1R analysis resulted in lower levels of energy expenditure (kcal/min) than 2R analysis utilizing hip data (S2) for both boys (P = 0.014) and girls (P = 0.047). Nine of 47 (S1) and 11/38 (S2) wrist, and 5/38 hip site monitors failed on upload; however complete or partial data were recovered by the manufacturer from 8 (S1) and 11 (S2) of the failed monitors. CONCLUSIONS: Wrist AC indicated that activity levels were similar during both sessions of camp. Anticipated comparison with DLW will determine which site and regression option provide a better representation of physical activity levels in overweight/obese adolescents. The high accelerometer failure rate resulted in design changes by the manufacture to decrease future problems when accelerometers are utilized for extended periods of time with this age group.