Organizations are facing the new challenge of integrating humans and robots into one cohesive workforce. Relational demography theory (RDT) explains the impact of dissimilarities on when and why humans trust and prefer to work with others. This paper proposes that RDT would be a useful lens to help organizations understand how to integrate humans and robots into a cohesive workforce. We proposed a research model based on RDT and examined dissimilarities in gender and co-worker type (human vs. robot) along with dissimilarities in work style and personality. To empirically examine the research model, two experiments were conducted with 347 and 422 warehouse workers. Results show that the negative impacts of gender, work style, and personality dissimilarities on swift trust depended on the co-worker type. Gender dissimilarity had a stronger negative impact on swift trust in a robot co-worker, while work style and personality had a weaker negative impact on swift trust in a robot co-worker. Also, swift trust in a robot co-worker increased the preference for a robot co-worker over a human co-worker, while swift trust in a human co-worker decreased such preferences. Overall, this research contributes to our current understanding of human–robot collaboration by identifying the importance of dissimilarity from the perspective of RDT.