The participants are instructed to remove the RT3 only for sleeping, bathing and swimming activities but some studies have shown the participants remove the accelerometer for longer times. The activities performed while the accelerometer is not being worn and, or energy that was not recorded during this time has never been estimated. This study aimed to assess compliance in using the accelerometer and quantify the energy expenditure (EE) not recorded by the accelerometer during the time it was not worn in free-living young males in a consecutive 4-day period. Eleven male participants 19 to 23 years of age, 54.7 to 85.5 kg with body mass index of 19.1 to 27.6 kg.m-2 completed the study. Resting metabolic rate was measured by indirect calorimetry. Daily EE estimation was on average 23.6% higher using the Bouchard Physical Activity Records than the RT3. Accelerometers were worn for 67 to 98% of waking hours but up to 30% of the EE was not recorded due to the device not being worn by participants mainly during intense physical activity. Recording the physical activity when the accelerometer is not being worn would provide a more precise estimative of the EE.