Crystal structure analyses are reported for anhydrous copper(II) hexafluoroacetylacetonate (Cu(hfac)(2)) and for two of its hydrates. The anhydrous compound (Cu(hfac)(2), 1: P (1) over bar; at 100 K, a = 5.428(1), b = 5.849(1), c = 11.516(3) Angstrom; alpha = 81.47(2), beta = 74.57(2), gamma = 86.96(2)degrees; Z = 1) contains centrosymmetric square-planar complexes with close intermolecular (CuF)-F-... contacts. The geometry of the complex is similar to that previously reported for Cu(hfac)(2)(.) toluene. The monoaquo compound (Cu(hfac)(2)(H2O), 2: P2(1)/c; at 100 K, a = 10.8300(8), b = 6.5400(6), c = 21.551(3) Angstrom; beta = 90.282(8)degrees; Z = 4) consists of square-pyramidal molecules with apical H2O ligands, and closelying F atoms in the sixth coordination sites. The major difference between this structure and the two other polymorphs previously reported is the nature and direction of hydrogen bonds. The yellow-green solid formed from Cu(hfac)(2) with excess H2O is identified as the trihydrate. In crystalline form it is the previously unreported [trans-Cu(hfac)(2)(H2O)(2)].H2O (3: P (1) over bar; at 150 K, a = 8.3899(3), b = 9.6011(3), c = 11.4852(4) Angstrom; alpha = 72.397(2), beta = 79.161(2), gamma = 87.843(2)degrees; Z = 2). There is no conclusive evidence in favor of any solid with the composition Cu(hfaC)(2). 2H(2)O.