Thirteen cyclic C2Si2H4 isomers, including disilatetrahedrane and the disilacyclobutadienes, have been studied by using ab initio quantum mechanics. At the MP3/6-31G* / /3-21G level of computation, the silyl-substituted silacyclopropenylidene is found to be the most stable. Disilatetrahedrane is quite high on the energy surface, and the two possible planar 1,2-disilacyclobutadienes do not represent minima on this surface. Planar 1,3-disilacyclobutadiene is a stable structure and exhibits significant diradical character.