Abstract: A process for the resolution of isomeric tramadol mixtures comprising: providing a purification stock comprising both cis and trans tramadol; contacting the purification stock with an acid under conditions effective to form an acid salt of the cis and trans tramadol in the purification stock; and separating the cis tramadol acid salt from the trans tramadol to obtain a purified cis tramadol acid salt; and optionally converting the cis tramadol acid salt to cis tramadol or to a pharmaceutically active salt thereof.