  We prove a monotonicity formula for mean curvature flow with surgery. This
formula differs from Huisken's monotonicity formula by an extra term involving
the mean curvature. As a consequence, we show that a surgically modified flow
which is sufficiently close to a smooth flow in the sense of geometric measure
theory is, in fact, free of surgeries. This result has applications to the
longtime behavior of mean curvature flow with surgery in Riemannian
three-manifolds.
