  In the Letter [PRL 102, 085703 (2009)] Brambilla, et al. claimed to observe
activated dynamics in colloidal hard spheres above the critical packing
fraction of mode coupling theory (MCT). By performing microscopic MCT
calculations, we show that polydispersity in their system shifts the critical
packing fraction above the value determined by van Megen et al. for less
polydisperse samples, and that the data agree with theory except for, possibly,
the highest packing fraction.
