(1) C25H33NO2Si, M(r) = 407.63, monoclinic, P2(1), a = 6.018 (2), b = 8.073 (3), c = 24.205 (4) angstrom, beta = 92.07 (2)degrees, V = 1175 (1) angstrom 3, Z = 2, D(x) = 1.152 Mg m-3, lambda(Mo K-alpha) = 0.71069 angstrom, mu = 0.1143 mm-1, F(000) = 440, T = 295 K, final R = 0.080 for 608 unique reflections [I > 2-sigma(I)]. (2) C25H33NO2Si, M(r) = 407.63, triclinic, P1BAR, a = 9.106 (3), b = 10.541 (4), c = 13.210 (3) angstrom, alpha = 79.20 (2), beta = 73.04 (2), gamma = 88.06 (3)degrees, V = 1191 (1) angstrom 3, Z = 2, D(x) = 1.137 Mg m-3, lambda(Mo K-alpha) = 0.71069 angstrom, mu = 0.1127 mm-1, F(000) = 440, T = 295 K, final R = 0.076 for 1188 unique reflections [I > 3-sigma(I)]. In both diastereoisomers the cyclohexane ring adopts a chair conformation, while the heterocycle prefers a quasi 1,2-diplanar conformation. They essentially differ in the relative configuration of the C(2)-H(2) and C(9)-H(9) bonds. The structural data are in good agreement with previous data obtained by H-1 NMR. There are no unusual bond lengths or angles.