The asymmetric unit of the title compound, C(9)H(11)ClN(4), contains two virtually planar mol-ecules that differ in conformation about the bond connecting the hydrazine and pyridazine units. The 3-chloro-6-hydrazinylpyridazine and cyclo-pentane groups are oriented at dihedral angles of 4.5 (3) and 8.8 (4)° in the two mol-ecules. In the crystal, the mol-ecules form a one dimensional polymeric structure extending along the a axis via N-H⋯N hydrogen bonds. The crystal stucired was an inversion twin [ratio of the twin domains = 0.73 (9):0.27 (9)].