The prevalence of overweight and obesity has risen rapidly worldwide, and the ongoing obesity pandemic is one of the most severe public health concerns in modern society. The average body mass index (BMI) of people living in Northern Norway has also steadily increased since the late 1970s. This study aims to understand how individuals’ health behavior is associated with the general health behavior of the people in their neighborhood. Using the population-based Tromsø Study, we examined the life course association between average leisure time physical activity at the neighborhood level and the BMI of individuals living in the same neighborhood. We used a longitudinal dataset following 25,604 individuals living in 33 neighborhoods and performed a linear mixed-effects analysis. Our results show a strong association between the average leisure time physical activity level of the neighborhood residents and higher BMI levels of residents of the same neighborhood. The results show that participants living in neighborhoods whose residents were more physically active during their leisure time, were likely to have a significantly lower BMI (-0.9 kg/m², 95% CI -1.5 to -0.4). Also, individuals living in neighborhoods whose residents were doing mainly manual work, had significantly higher BMI (0.7 kg/m², 95% CI 0.4 – 1.0).