In the molecule of the title compound, C50H49NO2, the acenaphtho[1,2-j]fluoranthene-4,5-dicarboximide framework has an approximately planar structure [maximum deviation = 0.124 (3) Å] and subtends a dihedral angle of 62.94 (8)° with the pendant phenyl group. Two of thetert-butyl groups are disordered over two sets of sites, with occupancy ratios of 0.506 (8):0.494 (8) and 0.669 (17):0.331 (17). An intermolecular short contact between a methyl group and the aromatic ring occurs in the crystal structure.