The crystal structures of 3,3-dinitroazetidinium, 1, and 1-i-propyl-3,3-dinitroazetidinium dinitramide, 2, have been determined. 1 crystallizes in the orthorhombic space group C m c21 with cell dimensions a = 9.932(1), b = 8.545(1), c = 11.107(1) Å, while 2 crystallizes in the orthorhombic space group Pbca with cell dimensions a = 11.464(2), b = 11.657(2), c = 17.916(4) Å. Compound 2 formed spontaneously from 1 by reacting with the solvent, acetone, during attempts to recrystallize it. The conformations adopted by the dinitramide ions are quite different with the bend, twist, and torsion angles for the dinitramide ion in 1 being much smaller than those in 2. Possible reasons for the dramatic differences in conformations observed in 1 and 2 are the different local symmetries for this ion found in the two structures as well as the absence of hydrogen bonding interactions in 2.