The title compound, C(7)H(7)N(11)O(11)·C(3)H(6)O, consisting of one mol-ecule of 10-formyl-2,4,6,8,12-penta-nitro-2,4,6,8,10,12-hexa-azatetra-cyclo-[5.5.0.0(5,9).0(3,11)]dodecane (penta-nitro-mono-form-yl-hexa-aza-isowurtzitane, PNMFIW) and one acetone solvent mol-ecule, is a member of the caged