Topic: A preliminary study on the reproducibility of results when mapping terms from an existing terminology to SNOMED CT post-coordinated expressions is described. Background: Implementing SNOMED CT requires a strategy for migrating existing systems and data that currently use other terminologies as well as ensuring that SNOMED CT contains suitable content that covers the domain. Mapping terms from these terminologies to SNOMED CT is one element of such a strategy. Snapper is a tool designed to assist in this complex task and enable the creation of quality mappings. Methods: Ten terms from the ANZICS diagnosis codes were selected to be mapped according to specified guidelines. The resulting mapping expressions were compared with each other and discussions were conducted with the mapping participants to determine issues they encountered during the process. Results: Consistency was easily achievable with mapping to single concepts, but was more difficult when mapping to post-coordinated expressions. The difficulties were traced to a lack of specificity in the supplied guidelines resulting in uncertainty in structuring the representation of compound concepts.