Concepts whose terms are of a similar word structure are expected to have similar logical representations. Anecdotal examples from SNOMED CT indicate that this may not always be the case. An investigation into the extent of inconsistent modeling in SNOMED CT hierarchies is carried out. A lexical methodology is used to identify sets of similar concepts. It is applied to one of the most attribute-rich hierarchies, Procedure, from which a random sample of 60 sets is derived. These sets are examined in regard to hierarchical, definitional, attribute, attribute/value, and role-group aspects. Thirty percent of the sample sets were found to have at least one type of modeling inconsistency. Their presence may interfere with the performance of terminology-driven applications. With the use of SNOMED expanding, such inconsistencies may eventually affect clinical care. Due to this, external auditing should be encouraged to identify such issues and complement IHTSDO's efforts.