  A subgroup $\Delta\leq \Gamma$ is commensurated if $|\Delta:\Delta\cap
\gamma\Delta\gamma^{-1}|<\infty$ for all $\gamma\in \Gamma$. We show a finitely
generated branch group is just infinite if and only if every commensurated
subgroup is either finite or of finite index. As a consequence, every
commensurated subgroup of the Grigorchuk group is either finite or finite
index.
