C11H10N2O, Mr = 186.22. Polymorph (I) monoclinic, P2(1)/c, a = 7.574 (1), b = 11.132 (2), c = 11.437 (2) A, beta = 94.90 (1) degree, V = 960.8 (5) A3, Z = 4, Dx = 1.287 Mg m-3, lambda(Mo K alpha) = 0.71069 A, mu = 0.079 mm-1, F(000) = 392, T = 293 K, R = 0.058 for 2335 observed reflections. Polymorph (II) monoclinic, P2(1)/c, a = 6.7897 (7), b = 13.449 (2), c = 10.736 (1) A, beta = 108.644 (8) degrees, V = 928.9 (2) A3, Z = 4, Dx = 1.331 Mg m-3, lambda(Mo K alpha) = 0.71069 A, mu = 0.082 mm-1, F(000) = 392, T = 293 K, R = 0.047 for 1952 observed reflections. The molecular conformations in the two polymorphs are similar and the torsion angle C(2)--C(1)--C(1')--C(2') is 58.9 (2) and 54.1 (2) degrees for (I) and (II), respectively. Both structures contain centrosymmetric hydrogen-bonded dimers of molecules with the pyridone ring NH groups acting as donors and the keto O atoms as acceptors with N...O distances of 2.776 (2) and 2.765 (1) A for (I) and (II), respectively.