The molecule crystallizes in a ketohydrazone tautomeric form. The tautomeric form is stabilized by a strong intramolecular hydrogen bond of 2.709(2)Angstrom binding the 3-oxo to the nearest nitrogen atom in the azine chain. The compound crystallizes in the monoclinic space group P2(1)/c with a = 7.0470(4), b = 11.3090(9), c = 16.2250(4)Angstrom, beta = 90.310(3)degrees, V = 1293.0(1)Angstrom(3), Z = 4, Dx = 1.3576 g cm(-3) and mu(Cu-K alpha) = 7.03 cm(-1). The molecule is nearly planar not regarding the methyl group; the small deviations from planarity are indicative of intramolecular interactions between the phenylazo group and indandione group. Some of the bond lengths and angles found in the molecule are distorted due to resonance, pi-electron delocalization and strain. The relation between these chemical effects and structural results are discussed.