Background: The purpose of the study is to evaluate age and gender differences in objectively measured levels of physical activity (PA) in a large and diverse sample of residents from an urban area in Porto, Portugal. Methods: Participants included 822 residents, 334 males (41%), and 488 females (59%), aged 6 to 90 years. GT1M accelerometer was used to assess daily PA over 7 consecutive days, and the measurement was from October (2007) to June (2008). Results: Males were more active than females. This difference was attenuated in the 2 oldest age groups (40-59 and 60+ yrs). An accentuated declined in all PA variables occurred between the youngster group (6-11 yrs) and adolescents group (12-19 yrs). Surprisingly, young adults (20-39 yrs) engaged in more moderate-to-vigorous PA (MVPA) than adolescents. Further, females also had higher MVPA in the fourth group (40-59 yrs) compared with the second group (12-19 yrs). Males had higher compliance rates of PA guidelines than females regardless the age group considered. Adolescents had very low compliance rates (females = 18.18%; males = 33.50%). Conclusions: Porto metropolitan area residents had low rates of compliance with current PA guidelines. A low level of PA in Porto adolescents is a matter of concern and suggests that interventions are needed.