The College of American Pathologists and the National Health Service (NHS) in the United Kingdom are merging their respective clinical terminologies, SNOMED RT and Clinical Terms Version 3, into a new terminology, SNOMED CT. This requires mapping concept descriptions between the two existing terminologies. During the mapping process, many descriptions were identified as being potentially problematic. They require further review by the SNOMED editorial process before either (1) being incorporated into SNOMED CT, or (2) retired from active use. This article presents data on the concept descriptions that were identified as needing further review during the early phases of SNOMED CT development. Based on this work, we describe fourteen types of problematic terminology content. Identifying problematic terminology content can be approached in a systematic manner.