The SM5.42 solvation model is extended to include compounds containing Si. The new parameters are based on a data set of 13 octanol/water partition coefficients (which we convert into 13 differential free energies of solvation), three absolute solvation energies, and one pK(a). The data set includes compounds containing C, H, 0, and Si. We carried out parametrizations using compounds in the data set that do not contain bonds between Si and O (i.e., eight differential free energies of solvation and three absolute free energies of solvation for nine compounds) at the HF/MIDI!, HF/MIDI!6D, HF/6-31G*, HF/6-31+G*, HF/cc-pVDZ, BPW91/MIDI!, BPW91/MIDI!6D, BPW91/DVZP, B3LYP/MIDI!, AMI, and PM3 levels of theory. The mean unsigned errors over the eight differential free energies of solvation and three absolute solvation energies for these levels of theory are in the range of 0.48-0.53 kcal/mol. We used five additional differential free energies of solvation for five compounds that do contain O-Si bonds to parametrize the BPW91/6-31G* level of theory. The resulting mean unsigned error over all 13 differential free energies of solvation and absolute free energies of solvation is 0.44 kcal/mol for this level of theory.