The present invention relates to novel crystalline forms of carbamoyl-cyclohexane derivatives and, more particularly, to novel co-crystalline forms of trans-1{4-[2-[4-(2,3-dichlorophenyl-piperazin-1-yl]-ethyl]-cyclohexyl}-3,3-dimethyl urea hydrochloride and an acid such as fumaric acid. Processes for preparing these forms, compositions containing these forms, and methods of use thereof are also described.