The title salt, C(9)H(18)NO(+)·C(7)H(3)ClNO(4) (-), was obtained as an unexpected product of the reaction of 4-chloro-3-nitro-benzoyl isothio-cyanate with pyrrolidine. The six-membered ring of the 4-oxopiperidinium cation adopts a chair conformation. In the crystal structure, two cations and three anions are linked together by inter-molecular N-H⋯O and C-H⋯O hydrogen bonds and arranged diagonally along the ac face.