The syntheses and X-ray crystal structures of 9-acetyl-o-carborane (1) and 9-cyano-o-carborane (2) are reported. In the crystal, molecules of 1 and 2 associate in one-dimensional polymeric chains or ct-type hydrogen-bonded networks linked through C-H-carborane... O or C-H-carborane... N hydrogen bonds, which provides further structural evidence for carboranes as a new class of proton donors in hydrogen-bond formation and attests to the ability of carborane moieties to participate in self-assembly processes.