In the title compound {systematic name: 2-[(E)-but-2-en-1-yl]isoindoline-1,3-dione}, C(12)H(11)NO(2), the phthalimide ring system is essentially planar, with a maximum deviation of 0.008 (1) Å, while the plane of the N-crotyl substituent is orthogonal to the phthalimide ring system, making a dihedral angle of 87.5 (1)°.