Background: Body mass index (BMI) may cluster in space among adults and be spatially dependent. Whether BMI clusters among children and how adults and children BMI clusters are related remains unknown. We aimed to identify and to compare BMI spatial dependence in adults and children in a Swiss general population, taking into account area's income level. Methods: Geo-referenced data from the Bus Santé study (adults, n=6,663) and Geneva School Health Service (children, n=3,601) were used. We implemented global (Moran's I) and local (Local Indicators of Spatial Association) indices of spatial autocorrelation to investigate the spatial dependence of BMI in adults (35-74 yrs) and children (6-7 yrs). Weight and height were measured using standardized procedures. Five spatial autocorrelation classes (LISA clusters) were defined including the high-high BMI class (high participant's BMI value correlated with high neighbors' mean BMI values). The spatial distributions of clusters were compared between adults and children with and without adjustment for area's income level. Results: In both adults and children, BMI was clearly not distributed at random across the State of Geneva. Both adult and children BMIs were associated with the mean BMI of their neighborhood. We found that clusters of higher BMI in adults and children are located in close, yet different, areas of the state. Significant clusters of high versus low BMIs were clearly identified in both adults and children. Area's income level influenced children BMI clusters. Conclusions: BMI clusters show a specific spatial dependence in adults and children from the general population. Using a fine scale spatial analytic approach, we identified life course specific clusters that could guide tailored interventions.