This article discusses many general and particular aspects concerning the primary key selection in relational databases. Considering the essential role of the primary key in designing relational models, the article sustain that making the correct selection will influence not only the consistency and coherence of information, but also all other related concepts: foreign keys, normal forms and referential integrity. Therefore, choosing the best solution for primary keys will affect on long term the entire database model. The paper identifies specific issues and makes comparative analysis for the main practices in primary key selection. Also, we expose the consequences that arise from choosing a primary key as it will be reflected in the future evolution of the database model.