ABSTRACT: BACKGROUND: Most accelerometers are worn around the waist (hip or lower back) to assess habitual physical activity. Wrist-worn accelerometers may be an alternative to the waist-worn monitors and may improve compliance in studies with prolonged wear. The aim of this study was to validate the Vivago[REGISTERED SIGN] Wrist-Worn Accelerometer at various intensities of physical activity (PA) in adults. METHODS: Twenty-one healthy adults aged 20--34 years were recruited for the study. Accelerometer data and oxygen uptake (VO2) were measured at sedentary, light, moderate and vigorous levels of PA. RESULTS: Activity categories and accelerometer counts were: sedentary, 0--15 counts[DOT OPERATOR]min[MINUS SIGN]1; light, 16--40 counts[DOT OPERATOR]min[MINUS SIGN]1; moderate, 41--85 counts[DOT OPERATOR]min[MINUS SIGN]1; and vigorous activity, > 85 counts[DOT OPERATOR]min[MINUS SIGN]1. ANOVA repeated measures was used to determine the relationship between accelerometry data output and oxygen consumption (r = .89; p < .001). The Bland and Altman method showed good agreement in the assessment of energy expenditure between the indirect calorimetry and the data obtained by the accelerometer. CONCLUSIONS: Results of the study suggest that the Vivago[REGISTERED SIGN] wrist-worn accelerometer is a valid measure of PA at varying levels of intensity. The study has also defined threshold values at four intensities and hence the Vivago[REGISTERED SIGN] accelerometer may be used to quantify PA in free living conditions among adults. This device has possible application in treating a variety of important health concerns.