Research has revealed that regular physical activity (PA) positively affects health. Accurate measurement of physical activity levels among adults is thus required. Recall questionnaires can obtain this in formation but retrieval of accurate in formation is known to be difficult. Accuracy can be enhanced by developing questionnaires that use cognitive techniques and recall cues. This researchde signed a valid and reliable past-seven -day Physical Activity Recall Questionnaire ( P A R Q ), using a model from cognitive psychology. This model explains the memory processesused to answer questions and identifies recall cues that can enhance accuracy. A draft version of PARQ was developed in study one. Items were gene rated following discussions in eight focus groups, conducted in both urban and rural settings. Following analysis of transcripts, descriptions of physical activity -related terms and a variety of recall cues, such as psychological and physiological descriptions, were included in the design of the draft PARQ. The cognitive processes used to complete the questionnaire we reassessed through a series of cognitive interviews, in study two. Identification of cognitive problems in the questionnaire was facilitate by applying Tourangeau’s (1984) model of the question -answer process, during data collection and analysis. Problematic areas, detected in the comprehension and retrieval stages or answering the question, were amended. This produced an improved version of PARQ that was ready for psychometrice valuation. The test-re test reliability of PARQ was comprehensively assessed in study three. Initially, intraclass correlations (0.95) indicated that PARQ is a highly reliable PA measurement tool. High intensity actvity and moderate intensity are equally reliable (0.94). Reliability was better when PARQ included a personal calendar (PC) recall cue (0.95) again st when the PC was not included (0.83). The order of questions in the questionnaire was assessed and found not to significantly affect there liability of PARQ. There liability of PARQ in measuring total, high and moderate intensity physical activity was further asserted, with similar results emerging following analysis by Pearson correlation coefficients and the Coefficient of Repeatability. Assessment of specific types of PA showed that the category with the least amount be recalled was the most reliable (family activity = 0.97). As the volume of recalled activity increased, correlation scores reduced. This reflects Conway’s description of the burden some retrieval of frequently performed memories, due to the structure of autobiographical memory. The final study examined the criterion validity of PARQ, firstly with an RT3 accelerometer (r= 052). The performance of asubmaximal walking treadmill test by each of the participants enabled the assessment of the individual intensity questions. A time -matched heart rate monitor and accelerometercon currently assessed the criterion validity of high intensity (r= 0 5 5 ) and moderate intensity (r=04) Concurrent validity of PARQ with the Stages of Change model of intentional behaviour change was also established, with regularly active participants reporting more activity than the not- regularly active participants. The ability of PARQ to provide valid in formation about the duration and intensity of different types of activities, means that it is capable of proving in formation about energy expenditure. This is important in terms of measuring the dose -response relationship between health and physical activity participation. The personal calendar acts as a recall cue that success fully probes the memory to retrieve accurate information. The application of the cognitive model to the design of PARQ has produced a reliable and valid working questionnaire. It directly provides accurate in formation about minutes of PA participation and indirectly provides information about energy expenditure, both of which are relevant to health - related guidelines, published by the American College of Sports Medecine and the Centre for Disease Control.