The use of SNOMED CT as a standard reference terminology enables interoperability between clinical systems. This reference tool provides a method for creating post-coordinated terms by users according to local needs. While the creation of these terms is free, there are a number of rules, as defined in the user manual of SNOMED CT that must be followed.The Hospital Italiano of Buenos Aires has a Terminology Server that encodes medical terms, using SNOMED CT as the reference vocabulary. An interoperability analysis performed with the Nebraska Medical Center in 2006 found a high error rate (26%) in post-coordinated terms. Therefore, we implemented an automatic system of rules within the Terminology Server as defined in the user manual. Following rules implementation, the error rate decreased from 26% to 2%.