Abstract:This study aimed to translate, adapt and validate the Yale Physical Activity Survey (YPAS) to Portuguese culture in order to assess the level of physical activity in a country with one of the world's highest percentage of senior citizens. Permission was obtained from the original authors and translated according to WHO guidelines. Validation included 471 older adults (70.3% women; 74.9±6.5 years), covering Criterion Validity, through Spearman's rho, with a cross-reference standard, by accelerometry with 96 subjects; and Reliability comprising Internal Consistency through Cronbach's alpha with 471 subjects, and Temporal Stability through Intraclass Correlation Coefficient involving 30 subjects. YPAS-PT appeared suitable and relevant with low-to-moderate levels for all psychometric parameters. Significant correlations were found for all variables, including accelerometer data ranging from 0.201 to 0.452 (p<0.001). Internal consistency (α≥0.835) and temporal stability (ICC>0.75) demonstrated high reliability. The YPAS-PT is a valid instrument to assess Physical Activity patterns of Portuguese older adults, allowing record low-intensity activities typical of sedentary behavior, which is often excluded from other Physical Activity assessment tools. The study has concluded that the Portuguese version of YPAS (i.e., YPAS-PT) is a valid instrument to assess PA patterns of Portuguese older adults for research and social interventions.