Ultrathin films of a low-molecular-weight block copolymer spontaneously dewet after several days at ambient temperature. Film rupture produces macroscopic holes and a residual pancake brush layer approximate to2 nm thick with intermittent mounds measuring up to 25 nm in thickness. Multiscale dewetting likewise occurs when the films are heated and returned to ambient temperature. Regardless of the surface pattern that forms during heating, submicron mounds develop on the dewetted copolymer film, and fine hoes emerge along the substrate surface after cooling.