The asymmetric unit of the title compound, C(18)H(23)BrClN(3)O(2), consists of two mol-ecules which exhibit different conformations of the pentyl chains [C-C-C-C torsion angles of -60.4 (4) and 175.8 (3)°]. The crysal packing exhibits a chain structure, generated through the O atom of the pyridazinone forming a hydrogen bond with the N-H group of an adjacent mol-ecule.