The destabilization of confined ultrathin poly(styrene-block-paramethylstyrene) films with a fully deuterated polystyrene block in the strong segregation limit is investigated. Using the spin-coating technique, polymer films with thicknesses smaller than the radius of gyration of the unperturbed polymer molecule were prepared on top of solid substrates. Successively these films have been annealed by storage under a toluene atmosphere. The evolving surface topographies are investigated with atomic force microscopy. From grazing incidence small-angle neutron scattering (GISANS), the microphase separation structure is determined in addition. Although these ultrathin films are hardly detectable with reflectivity measurements, in GISANS a good signal was obtained. The time dependence of the characteristic lateral length of the nanostructures follows an Avrami growth law.