The x-ray crystal structure anal. of tris(trimethylsilyl)cyclopropenylium cation 2 is presented and compared with the structure and bonding properties obtained by quantum mech. ab initio calcns. The calcd. bond lengths for 2 are in good agreement with the exptl. detd. ones. The effect of tris-silyl and tris-Me substitution on the stability of the tris-substituted cyclopropenylium ions are calcd. by using the isodesmic hydride transfer reaction. The pKR+ value of 2 is predicted to be 4.