Plant organ size is limited by genetic constraints, however, relatively few organ size regulators have been identified. Among them, the BIG BROTHER (BB) gene has a prominent role in the determination of leaf(-like) organ size. In this issue, Cattaneo and Hardtke (on pp.1519-1527) show that BB also plays a role underground; bb loss-of-function mutants display increased root meristem size due to an increased number of meristematic cells and also formative divisions, while mature cell length is unaffected. Thus, bb mutations uncouple cell proliferation from elongation in the root meristem and reveal a role for BB in dampening root cell divisions.