. C4H2CI2N:O, Mr= 164.99; form (1): mono­clinic,  P21/c,  a = 5.1967 (12), b = 9.046 (2), c = 12.901 (3) Å,  β= 100.090 (15)°,   V = 597.1 (2) Å3, Z=4,Dx= 1.84g cm-3,Mo Ka, λ=0.71069 Å, µ= 9.93 cm -1, F(000) = 328, T= 163 K, R = 0.028 for 1552 reflections; form (II): monoclinic, P21 /c, a = 5.3384 (7), b = 13.827 (2), c = 7.9107 (12)Å, β=94.397 (14)°, V = 582.20 (14) A3 Z = 4, Dx = 1.88 g cm-3, Mo Ka, λ = 0.71069 Å, µ = 10.18 cm -1, F(000) = 328, T= 163 K, R = 0.025 for 1597 reflec­tions. The compound, in each form, exists in the oxo form and crystallizes as hydrogen-bonded dimers. Infinite layers of dimers result from C-H ... O- and C –H...CI-type H bonds for forms (I) and (II), respectively [H...O 2.25 (2), C…O 3.076 (2); H---CI 2.74 (2), C---CI 3.534 (1) Å]. There are only minor differences in the bond distances and angles of the two forms.