Deliberation among judges plays a central role in the judicial decision-making process of collegial courts. The quality of such deliberation is therefore essential to successful adjudication. In this paper I argue that collegial deliberation works better when judges are more familiar with each other. Relying on a novel dataset of appeals in criminal cases at the German Federal Court of Justice I exploit quasi-random assignment of cases to decision-making groups to show that familiarity substantially increases the probability that judges schedule a main hearing after first- stage deliberations. I conclude that the quality of adjudication can be improved by structuring debate such that it imposes the least conformity pressure. Furthermore, rules that govern the groups’ composition should promote familiarity between as many judges as possible.