To evaluate the accuracy of a Functional Activity Monitor (FAM) in 1) detecting daily activities including postures (sitting, standing, lying), transfers between postures and walking, and 2) measuring activity duration and step frequency. A cross-sectional study comparing the outcomes of the FAM to 1) video recordings (HS100P/PC, Panasonic Inc. and VIXIA HG21, Canon Inc.) for activity identification, and 2) 3D motion analysis system recordings (Optotrak 3020 NDI) for measuring step frequencies. The FAM includes one triaxial accelerometer, and one triaxial gyroscope, powered by 3.7V lithium ion battery (sample frequency of 50 Hz; Sparkfun Inc, Boulder CO, USA). One FAM was positioned on the sternum and two on each thigh. Wireless transmission of data to a PDA (Motorola Inc.) was established by means of Bluetooth. Trials included postures, transfers between postures and walking at preferred, slow and fast speeds. Statistical analysis included the determination of percentage of agreement and an ANOVA with repeated measures. Clinical Movement Sciences Laboratory, Boston University. Ten young adults (range 20-26 years of age) including 5 males and 5 females. Not applicable. Frequency of occurrence of activities, activity duration and step frequencies. The agreement between tools for identification of postures ranged from 96.2% to 100%, and for the identification of transfers and walking from 98.6% to1:00%. There was no significant difference between tools in terms of activity duration and step frequencies at different walking speeds. The FAM is an accurate device to monitor daily functional activities, activity durations and step frequencies of healthy young adults in research lab settings. Future research will focus on the validation of the FAM in the evaluation of daily activities of elderly in their home and community environment.