The selection of appropriate vocabulary is a crucial and challenging aspect of augmentative and alternative communication (AAC) intervention. Core vocabulary lists are frequently used to support vocabulary selection for children who require AAC. A vocabulary domain that has garnered limited attention within the AAC literature is relational basic concepts (RBCs). RBCs describe relationships between objects, persons, or situations, and play a pivotal role in language development, communication, and academic success. For the present study, we created a list of 156 RBCs, drawing primarily from assessments that measure basic concept knowledge in preschool and early elementary school students. We examined the overlap of these words on nine core vocabulary lists. We found that most concepts were not represented on any core lists. Additionally, there was relatively little overlap of RBCs between the core lists. These findings suggest that vocabulary selection resources created using exclusively a core vocabulary approach may have limited utility for identifying many concepts that preschool and early elementary students are expected to know and use. Implications for AAC research and practice are discussed with emphasis on the need for further consideration of RBCs within vocabulary selection practice and the field of AAC at large.