The international criminal courts and tribunals have heard thousands of witnesses in cases of extreme complexity and breadth. Their evidentiary record is overwhelming, with live witness testimony standing out as one of its defining features. Keeping in mind the arguments and policies of judicial efficiency and fairness, this article empirically examines the trends and patterns in viva voce witness numbers at the International Criminal Tribunal for the Former Yugoslavia (ICTY), for Rwanda (ICTR), and the International Criminal Court (ICC). We observe clear differences between institutions and individual cases, and discuss the underlying reasons for such divergences. As well as providing a general overview, we demonstrate the complex interaction between case-related characteristics, institutional and situational contexts, and the number of witnesses called at trial.