In the title compound, C(18)H(20)N(2)O(3), the dihedral angle between the indole ring system (r.m.s. deviation = 0.018 Å) and the hy-droxy-methyl-enepyrrolidine-2,4-dione plane (r.m.s. deviation = 0.036 Å) is 9.87 (7)°. The keto and enol groups are involved in an intra-molecular O-H⋯O hydrogen bond. An intra-molecular C-H⋯O inter-action also occurs. The sec-butyl group is disordered over two orientations corresponding to an approximate 180° rotation about the N-C bond, with occupancies of 0.670 (6) and 0.330 (6). In the crystal, mol-ecules are linked into chains along the c axis by C-H⋯O hydrogen bonds.