The ability of the SenseWear Armband (SWA) to estimate energy expenditure (EE) in adults is established. However, except for resting metabolic rate, the test-retest reliability of the SWA for the estimation of EE in adults is unknown. To explore reliability, 34 healthy adults (50% women; age, 26.7 ± 6.1 years; body mass index, 23.6 ± 3.3 kg·m(-2)) completed a 2-day study protocol. During 13 h of direct supervision, subjects completed, each day, 60 min of lying awake rest, 30 min of structured sedentary activity, 45 min of walking circuit, and 45 min of ergocycling at 50% of their peak oxygen uptake. For the remaining 10 h, subjects remained seated. The SWA showed significant intraclass correlations between the 2 days of testing for the overall 13 h of direct supervision (r = 0.97; p < 0.001), the lying awake rest (r = 0.98; p < 0.001), the structured sedentary activity (r = 0.62; p < 0.05), the walking circuit (r = 0.95; p < 0.001), and the standardized physical activity (r = 0.85; p < 0.001). The results of this study indicate that the SWA is a reliable tool to estimate EE during multiple activities. These data provide additional evidence of the usefulness of the SWA in monitoring EE in healthy adults.