According to a substantial body of evidence, regular physical activity can bring significantrnhealth benefits to people of all ages and abilities. Scientific evidence increasingly indicatesrnthat physical activity can extend years of active independent living, reduce disability andrnimprove the quality of life of young and older adults. Despite these evidences, little is knownrnabout physical activity or its measurement on a population basis.rnA cross-sectional community based study was conducted to assess reliability and validity ofrninstruments for measuring levels of physical activity. The instrument with better reliabilityrnand validity was used to measure levels and assess determinants of physical activity.rnSimple random sampling was carried out to recruit a total of 940 subjects. Global PhysicalrnActivity Questionnaire (GPAQ) and International Physical Activity Questionnaire (IPAQ)rnwere administered to all participants during the first contact. The questionnaires werernadministered again after 4 days to a randomly selected sub-sample of 151 participants inrnorder to assess reliability. Validity of the questionnaires was assessed on another randomlyrnselected group of 186 study participants who wore motion monitor for seven consecutiverndays.rnA set of reliability tests indicated that GPAQ and IPAQ had good repeatability; balance inrnfavor of the former. Validity of the questionnaires was assessed by a number of methods.rnUnlike reliability, validity was modest: percent correctly classified by concurrent validity ofrnGPAQ against IPAQ for various domains of activity was between 35.9 and 42.5; grossrnviirnmisclassification was in the range 17.7-26.3%. In criterion validity test of the questionnairesrnagainst motion monitor, percent correctly classified was between 21.0 and 35.5 for GPAQrnand between 25.3 and 38.2 for IPAQ; gross misclassification was in the range of 21.1-40.3%rnfor GPAQ and 18.3-41.9 for IPAQ. The prevalence of physical activity measured by GPAQrnwas found to be 77%(724/940).rnCumulative assessment of reliability and validity of questionnaires used in this studyrnindicated that GPAQ and IPAQ were appropriate for use in our setting. However, conductingrnsimilar reliability and validity studies across different seasons and regions is stronglyrnrecommended before applying them on large-scale studies