This article returns to the discussion about the possible deterrent effect of the International Criminal Court. It argues that previous discussions are incomplete as they fail to take into account the significance specifically for deterrence of differences between prosecuting in bello and ad bellum atrocity crimes. To this end, the paper focuses on the recent activation of the Court’s jurisdiction over the crime of aggression and sees this fact in combination with reports about the behavior of the prime ministers of both the United Kingdom and Denmark leading up to the 2003 invasion of Iraq. Thus, before taking their countries to war, both Tony Blair and Anders Fogh Rasmussen asked their respective legal advisors whether in joining the US-led war they would run the risk, as individuals, of being brought before the ICC. When seen in light of the recent activation of the crime of aggression, the fact that both heads of state felt compelled to ask this particular question at that particular point in time is highly interesting because it both lends support to, points to important lacunae in, and adds nuance to the deterrence-based argument in favor of the ICC.