Crystals of Rb-TCNQ have monoclinic symmetry; the space group is P2t/c, a = 7-187 (1), b = 12.347 (2), c= 13.081 (3) A, fl=98"88 (2) °, Z=4. Rb + and TCNQ-are both at general positions. The intensities were collected at -160°C on an automatic Nonius diffractometer. Approximate values for the atomic coordinates were obtained from Patterson and difference Fourier maps. Anisotropic least-squares refinement decreased the residual R to 0.066 for 5512 independent reflexions. The bond lengths in the TCNQ-ion show that the ion has quinoid character; the group is not planar but has the shape of a shallow boat. The TCNQ-radical-ions form charge-resonance bounded rows along the a axis. The interaction between the rows is small. Within a row interplanar spacings of 3" 159 and 3"484/~, alternate. The distance of 3"159 ~ is the shortest distance found so far between successive TCNQ planes. The Rb + ions also form rows along the a axis with alternating distances of 3-483 and 3.726 A between the ions. These distances are appreciably longer than twice the radius of Rb ÷ (3.0 A). Rb + is octahedrally surrounded by eight negatively charged TCNQ nitrogen atoms at distances of 2. 982, 2.996, 3.004, 3.009, 3.025, 3.055, 3.057 and 3.108 ~.