Understanding population prevalences of physical activity is important to develop benchmarks for current baseline levels to monitor future changes, and for making country/regional comparisons. The purpose was to review the global prevalence of physical activity levels among youth and adults. Standardized literature searches for articles about national prevalences of physical activity were conducted in PubMed. A total of 34 studies in adults and 28 studies in youth were deemed contemporary (1996 - present) and met the inclusion criteria for this review. Wide variability was present between countries in the prevalence of physical activity (as measured and defined by individual studies). Studies with the highest reported prevalences of physical activity were for men in Sweden (77%), women in Denmark (81%), 12- to 15-year-old boys in Australia (74%) and <12-year-old girls (75%) in China. The countries with the lowest reported prevalences of physical activity were men in Brazil (4%), women in Saudi Arabia (2%) and Thailand (2%), and 17- to 18-year-old boys (0%) and 17- to 18-year-old girls (0%) in Russia. The ranges of prevalence of physical activity, mode of data collection, and determination of meeting the physical activity threshold vary greatly between countries. However, the aggregation of these data can be a useful resource to practitioners, interventionists and epidemiologists.