Synthesis, single-crystal structure determination, and magnetic properties are reported for manganese carbodiimide, MnNCN. The presumably unstable but inert phase adopts the trigonal system (R $(3) over bar $m) with a = 3.3583(4) angstrom, c. = 14.347(2) angstrom, V = 140.13(3) angstrom(3), and Z = 3. Divalent manganese is octahedrally coordinated by nitrogen atoms at 2.26 angstrom, and the NCN2- unit adopts the linear [N=C=N](2-) carbodiimide shape with two C=N double bonds of 1.23 angstrom. MnNCN contains high-spin Mn(II) with five unpaired electrons and behaves like an antiferromagnet with an ordering temperature below 30 K.